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 $61.66   5.258%   $64.9021   $64.90   $64.90   $64.90  
  Purchase #2 $24.51   9.834%   $26.9203   $26.92   $26.90   $26.90  
  Purchase #3 $153.99   11.237%   $171.2939   $171.29   $171.30   $171.30  
  Purchase #4 $188.84   13.629%   $214.577   $214.58   $214.60   $214.60  
  Purchase #5 $141.79   12.645%   $159.7193   $159.72   $159.70   $159.70  
  Purchase #6 $221.54   11.136%   $246.2107   $246.21   $246.20   $246.20  
  Purchase #7 $216.52   9.633%   $237.3774   $237.38   $237.40   $237.40  
  7 purchase totals = $1,008.85       $1,121.0007   $1,121.00   $1,121.00   $1,121.00