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 $89.79   5.260%   $94.513   $94.51   $94.50   $94.50  
  Purchase #2 $219.91   9.472%   $240.7399   $240.74   $240.75   $240.70  
  Purchase #3 $24.75   4.744%   $25.9241   $25.92   $25.90   $25.90  
  Purchase #4 $92.78   13.816%   $105.5985   $105.60   $105.60   $105.60  
  Purchase #5 $151.30   3.545%   $156.6636   $156.66   $156.65   $156.70  
  Purchase #6 $177.79   9.563%   $194.7921   $194.79   $194.80   $194.80  
  Purchase #7 $167.45   5.217%   $176.1859   $176.19   $176.20   $176.20  
  7 purchase totals = $923.77       $994.4171   $994.41   $994.40   $994.40