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 $60.78   12.454%   $68.3495   $68.35   $68.35   $68.30  
  Purchase #2 $176.74   11.763%   $197.5299   $197.53   $197.55   $197.50  
  Purchase #3 $113.79   9.818%   $124.9619   $124.96   $124.95   $125.00  
  Purchase #4 $107.61   8.151%   $116.3813   $116.38   $116.40   $116.40  
  Purchase #5 $245.67   4.356%   $256.3714   $256.37   $256.35   $256.40  
  Purchase #6 $165.62   11.438%   $184.5636   $184.56   $184.55   $184.60  
  Purchase #7 $198.38   4.373%   $207.0552   $207.06   $207.05   $207.10  
  7 purchase totals = $1,068.59       $1,155.2128   $1,155.21   $1,155.20   $1,155.30