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 $118.73   7.229%   $127.313   $127.31   $127.30   $127.30  
  Purchase #2 $141.29   13.311%   $160.0971   $160.10   $160.10   $160.10  
  Purchase #3 $14.86   7.486%   $15.9724   $15.97   $15.95   $16.00  
  Purchase #4 $60.47   13.379%   $68.5603   $68.56   $68.55   $68.60  
  Purchase #5 $51.96   8.853%   $56.56   $56.56   $56.55   $56.60  
  Purchase #6 $95.47   6.418%   $101.5973   $101.60   $101.60   $101.60  
  Purchase #7 $32.46   9.694%   $35.6067   $35.61   $35.60   $35.60  
  7 purchase totals = $515.24       $565.7068   $565.71   $565.65   $565.80