Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $189.65   13.677%   $215.5884   $215.59   $215.60   $215.60  
  Purchase #2 $195.45   4.207%   $203.6726   $203.67   $203.65   $203.70  
  Purchase #3 $248.66   9.642%   $272.6358   $272.64   $272.65   $272.60  
  Purchase #4 $229.46   5.121%   $241.2106   $241.21   $241.20   $241.20  
  Purchase #5 $161.93   13.687%   $184.0934   $184.09   $184.10   $184.10  
  Purchase #6 $116.47   6.840%   $124.4365   $124.44   $124.45   $124.40  
  Purchase #7 $117.92   10.127%   $129.8618   $129.86   $129.85   $129.90  
  7 purchase totals = $1,259.54       $1,371.4991   $1,371.50   $1,371.50   $1,371.50