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 $114.40   11.261%   $127.2826   $127.28   $127.30   $127.30  
  Purchase #2 $25.46   4.202%   $26.5298   $26.53   $26.55   $26.50  
  Purchase #3 $189.72   11.715%   $211.9457   $211.95   $211.95   $211.90  
  Purchase #4 $68.28   11.265%   $75.9717   $75.97   $75.95   $76.00  
  Purchase #5 $94.81   3.156%   $97.8022   $97.80   $97.80   $97.80  
  Purchase #6 $229.96   13.487%   $260.9747   $260.97   $260.95   $261.00  
  Purchase #7 $179.90   12.258%   $201.9521   $201.95   $201.95   $202.00  
  7 purchase totals = $902.53       $1,002.4588   $1,002.45   $1,002.45   $1,002.50