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 $60.46   9.535%   $66.2249   $66.22   $66.20   $66.20  
  Purchase #2 $217.71   11.849%   $243.5065   $243.51   $243.50   $243.50  
  Purchase #3 $151.43   11.600%   $168.9959   $169.00   $169.00   $169.00  
  Purchase #4 $175.90   8.503%   $190.8568   $190.86   $190.85   $190.90  
  Purchase #5 $125.75   6.727%   $134.2092   $134.21   $134.20   $134.20  
  Purchase #6 $173.72   4.142%   $180.9155   $180.92   $180.90   $180.90  
  Purchase #7 $11.71   8.773%   $12.7373   $12.74   $12.75   $12.70  
  7 purchase totals = $916.68       $997.4461   $997.46   $997.40   $997.40