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 $125.50   6.238%   $133.3287   $133.33   $133.35   $133.30  
  Purchase #2 $66.72   11.594%   $74.4555   $74.46   $74.45   $74.50  
  Purchase #3 $106.93   13.495%   $121.3602   $121.36   $121.35   $121.40  
  Purchase #4 $32.97   9.572%   $36.1259   $36.13   $36.15   $36.10  
  Purchase #5 $206.30   13.341%   $233.8225   $233.82   $233.80   $233.80  
  Purchase #6 $171.34   13.572%   $194.5943   $194.59   $194.60   $194.60  
  Purchase #7 $90.32   13.616%   $102.618   $102.62   $102.60   $102.60  
  7 purchase totals = $800.08       $896.3051   $896.31   $896.30   $896.30