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 $215.59   9.441%   $235.9439   $235.94   $235.95   $235.90  
  Purchase #2 $197.28   7.642%   $212.3561   $212.36   $212.35   $212.40  
  Purchase #3 $139.46   11.138%   $154.9931   $154.99   $155.00   $155.00  
  Purchase #4 $105.49   13.132%   $119.3429   $119.34   $119.35   $119.30  
  Purchase #5 $201.65   13.126%   $228.1186   $228.12   $228.10   $228.10  
  Purchase #6 $13.86   11.847%   $15.502   $15.50   $15.50   $15.50  
  Purchase #7 $93.74   12.724%   $105.6675   $105.67   $105.65   $105.70  
  7 purchase totals = $967.07       $1,071.9241   $1,071.92   $1,071.90   $1,071.90