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 $78.39   6.203%   $83.2525   $83.25   $83.25   $83.30  
  Purchase #2 $235.93   3.113%   $243.2745   $243.27   $243.25   $243.30  
  Purchase #3 $27.42   13.620%   $31.1546   $31.15   $31.15   $31.20  
  Purchase #4 $231.57   12.718%   $261.0211   $261.02   $261.00   $261.00  
  Purchase #5 $162.30   4.122%   $168.99   $168.99   $169.00   $169.00  
  Purchase #6 $206.56   13.550%   $234.5489   $234.55   $234.55   $234.50  
  Purchase #7 $11.70   4.136%   $12.1839   $12.18   $12.20   $12.20  
  7 purchase totals = $953.87       $1,034.4255   $1,034.41   $1,034.40   $1,034.50