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 $89.53   12.854%   $101.0382   $101.04   $101.05   $101.00  
  Purchase #2 $248.38   11.130%   $276.0247   $276.02   $276.00   $276.00  
  Purchase #3 $85.26   3.814%   $88.5118   $88.51   $88.50   $88.50  
  Purchase #4 $43.94   6.355%   $46.7324   $46.73   $46.75   $46.70  
  Purchase #5 $85.80   7.715%   $92.4195   $92.42   $92.40   $92.40  
  Purchase #6 $124.80   5.325%   $131.4456   $131.45   $131.45   $131.40  
  Purchase #7 $120.43   5.279%   $126.7875   $126.79   $126.80   $126.80  
  7 purchase totals = $798.14       $862.9597   $862.96   $862.95   $862.80