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 $205.66   13.181%   $232.768   $232.77   $232.75   $232.80  
  Purchase #2 $59.29   11.206%   $65.934   $65.93   $65.95   $65.90  
  Purchase #3 $150.48   4.340%   $157.0108   $157.01   $157.00   $157.00  
  Purchase #4 $195.81   7.469%   $210.435   $210.44   $210.45   $210.40  
  Purchase #5 $206.92   9.716%   $227.0243   $227.02   $227.00   $227.00  
  Purchase #6 $8.66   12.147%   $9.7119   $9.71   $9.70   $9.70  
  Purchase #7 $101.73   3.671%   $105.4645   $105.46   $105.45   $105.50  
  7 purchase totals = $928.55       $1,008.3485   $1,008.34   $1,008.30   $1,008.30