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 $49.43   13.524%   $56.1149   $56.11   $56.10   $56.10  
  Purchase #2 $113.92   10.309%   $125.664   $125.66   $125.65   $125.70  
  Purchase #3 $219.88   9.572%   $240.9269   $240.93   $240.95   $240.90  
  Purchase #4 $37.71   6.609%   $40.2023   $40.20   $40.20   $40.20  
  Purchase #5 $161.26   8.182%   $174.4543   $174.45   $174.45   $174.50  
  Purchase #6 $62.64   6.848%   $66.9296   $66.93   $66.95   $66.90  
  Purchase #7 $93.44   9.680%   $102.485   $102.49   $102.50   $102.50  
  7 purchase totals = $738.28       $806.7770   $806.77   $806.80   $806.80