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 $84.83   12.789%   $95.6789   $95.68   $95.70   $95.70  
  Purchase #2 $222.39   10.610%   $245.9856   $245.99   $246.00   $246.00  
  Purchase #3 $12.56   6.727%   $13.4049   $13.40   $13.40   $13.40  
  Purchase #4 $119.78   11.279%   $133.29   $133.29   $133.30   $133.30  
  Purchase #5 $108.96   8.361%   $118.0701   $118.07   $118.05   $118.10  
  Purchase #6 $189.74   13.131%   $214.6548   $214.65   $214.65   $214.70  
  Purchase #7 $54.73   10.333%   $60.3853   $60.39   $60.40   $60.40  
  7 purchase totals = $792.99       $881.4696   $881.47   $881.50   $881.60