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 $151.27   9.207%   $165.1974   $165.20   $165.20   $165.20  
  Purchase #2 $56.28   6.641%   $60.0176   $60.02   $60.00   $60.00  
  Purchase #3 $234.63   10.266%   $258.7171   $258.72   $258.70   $258.70  
  Purchase #4 $215.86   13.472%   $244.9407   $244.94   $244.95   $244.90  
  Purchase #5 $221.89   10.563%   $245.3282   $245.33   $245.35   $245.30  
  Purchase #6 $222.91   9.437%   $243.946   $243.95   $243.95   $243.90  
  Purchase #7 $30.49   6.370%   $32.4322   $32.43   $32.45   $32.40  
  7 purchase totals = $1,133.33       $1,250.5792   $1,250.59   $1,250.60   $1,250.40