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 $88.63   11.713%   $99.0112   $99.01   $99.00   $99.00  
  Purchase #2 $191.62   9.527%   $209.8756   $209.88   $209.90   $209.90  
  Purchase #3 $168.87   13.545%   $191.7434   $191.74   $191.75   $191.70  
  Purchase #4 $213.36   6.841%   $227.956   $227.96   $227.95   $228.00  
  Purchase #5 $57.44   9.539%   $62.9192   $62.92   $62.90   $62.90  
  Purchase #6 $14.63   4.869%   $15.3423   $15.34   $15.35   $15.30  
  Purchase #7 $223.83   10.504%   $247.3411   $247.34   $247.35   $247.30  
  7 purchase totals = $958.38       $1,054.1888   $1,054.19   $1,054.20   $1,054.10