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 $163.51   12.403%   $183.7901   $183.79   $183.80   $183.80  
  Purchase #2 $41.44   10.712%   $45.8791   $45.88   $45.90   $45.90  
  Purchase #3 $91.25   12.462%   $102.6216   $102.62   $102.60   $102.60  
  Purchase #4 $73.27   12.518%   $82.4419   $82.44   $82.45   $82.40  
  Purchase #5 $84.61   9.494%   $92.6429   $92.64   $92.65   $92.60  
  Purchase #6 $51.25   12.266%   $57.5363   $57.54   $57.55   $57.50  
  Purchase #7 $147.28   3.399%   $152.286   $152.29   $152.30   $152.30  
  7 purchase totals = $652.61       $717.1979   $717.20   $717.25   $717.10