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 $84.46   11.679%   $94.3241   $94.32   $94.30   $94.30  
  Purchase #2 $245.26   7.196%   $262.9089   $262.91   $262.90   $262.90  
  Purchase #3 $75.65   12.548%   $85.1426   $85.14   $85.15   $85.10  
  Purchase #4 $56.56   12.132%   $63.4219   $63.42   $63.40   $63.40  
  Purchase #5 $217.78   4.480%   $227.5365   $227.54   $227.55   $227.50  
  Purchase #6 $110.29   12.257%   $123.8082   $123.81   $123.80   $123.80  
  Purchase #7 $89.81   7.750%   $96.7703   $96.77   $96.75   $96.80  
  7 purchase totals = $879.81       $953.9125   $953.91   $953.85   $953.80