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 $81.59   13.840%   $92.8821   $92.88   $92.90   $92.90  
  Purchase #2 $183.62   6.601%   $195.7408   $195.74   $195.75   $195.70  
  Purchase #3 $87.91   4.584%   $91.9398   $91.94   $91.95   $91.90  
  Purchase #4 $114.32   13.151%   $129.3542   $129.35   $129.35   $129.40  
  Purchase #5 $200.99   6.298%   $213.6484   $213.65   $213.65   $213.60  
  Purchase #6 $51.63   11.313%   $57.4709   $57.47   $57.45   $57.50  
  Purchase #7 $59.56   7.545%   $64.0538   $64.05   $64.05   $64.10  
  7 purchase totals = $779.62       $845.0900   $845.08   $845.10   $845.10