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 $75.51   12.528%   $84.9699   $84.97   $84.95   $85.00  
  Purchase #2 $200.90   12.188%   $225.3857   $225.39   $225.40   $225.40  
  Purchase #3 $92.51   9.717%   $101.4992   $101.50   $101.50   $101.50  
  Purchase #4 $88.26   5.150%   $92.8054   $92.81   $92.80   $92.80  
  Purchase #5 $157.79   12.397%   $177.3512   $177.35   $177.35   $177.40  
  Purchase #6 $212.54   11.612%   $237.2201   $237.22   $237.20   $237.20  
  Purchase #7 $103.49   11.113%   $114.9908   $114.99   $115.00   $115.00  
  7 purchase totals = $931.00       $1,034.2223   $1,034.23   $1,034.20   $1,034.30