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 $162.29   13.654%   $184.4491   $184.45   $184.45   $184.40  
  Purchase #2 $97.85   3.577%   $101.3501   $101.35   $101.35   $101.40  
  Purchase #3 $143.47   10.307%   $158.2575   $158.26   $158.25   $158.30  
  Purchase #4 $221.72   6.112%   $235.2715   $235.27   $235.25   $235.30  
  Purchase #5 $217.84   13.396%   $247.0218   $247.02   $247.00   $247.00  
  Purchase #6 $242.35   3.136%   $249.9501   $249.95   $249.95   $250.00  
  Purchase #7 $64.93   10.389%   $71.6756   $71.68   $71.70   $71.70  
  7 purchase totals = $1,150.45       $1,247.9757   $1,247.98   $1,247.95   $1,248.10