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 $36.53   13.683%   $41.5284   $41.53   $41.55   $41.50  
  Purchase #2 $149.99   7.631%   $161.4357   $161.44   $161.45   $161.40  
  Purchase #3 $98.30   3.246%   $101.4908   $101.49   $101.50   $101.50  
  Purchase #4 $237.33   3.627%   $245.938   $245.94   $245.95   $245.90  
  Purchase #5 $187.55   3.445%   $194.0111   $194.01   $194.00   $194.00  
  Purchase #6 $153.64   11.199%   $170.8461   $170.85   $170.85   $170.80  
  Purchase #7 $39.85   11.742%   $44.5292   $44.53   $44.55   $44.50  
  7 purchase totals = $903.19       $959.7793   $959.79   $959.85   $959.60