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 $211.56   11.792%   $236.5072   $236.51   $236.50   $236.50  
  Purchase #2 $34.96   13.574%   $39.7055   $39.71   $39.70   $39.70  
  Purchase #3 $70.92   4.712%   $74.2618   $74.26   $74.25   $74.30  
  Purchase #4 $247.27   12.199%   $277.4345   $277.43   $277.45   $277.40  
  Purchase #5 $215.91   6.658%   $230.2853   $230.29   $230.30   $230.30  
  Purchase #6 $242.78   7.653%   $261.36   $261.36   $261.35   $261.40  
  Purchase #7 $33.70   6.137%   $35.7682   $35.77   $35.75   $35.80  
  7 purchase totals = $1,057.10       $1,155.3225   $1,155.33   $1,155.30   $1,155.40