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 $190.44   4.711%   $199.4116   $199.41   $199.40   $199.40  
  Purchase #2 $150.30   10.514%   $166.1025   $166.10   $166.10   $166.10  
  Purchase #3 $177.57   5.608%   $187.5281   $187.53   $187.55   $187.50  
  Purchase #4 $84.84   4.672%   $88.8037   $88.80   $88.80   $88.80  
  Purchase #5 $7.44   9.253%   $8.1284   $8.13   $8.15   $8.10  
  Purchase #6 $87.34   13.873%   $99.4567   $99.46   $99.45   $99.50  
  Purchase #7 $148.56   8.709%   $161.4981   $161.50   $161.50   $161.50  
  7 purchase totals = $846.49       $910.9291   $910.93   $910.95   $910.90