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 $25.57   11.717%   $28.566   $28.57   $28.55   $28.60  
  Purchase #2 $124.96   7.190%   $133.9446   $133.94   $133.95   $133.90  
  Purchase #3 $164.69   8.108%   $178.0431   $178.04   $178.05   $178.00  
  Purchase #4 $216.99   6.157%   $230.3501   $230.35   $230.35   $230.40  
  Purchase #5 $48.43   12.182%   $54.3297   $54.33   $54.35   $54.30  
  Purchase #6 $74.97   11.437%   $83.5443   $83.54   $83.55   $83.50  
  Purchase #7 $240.60   3.129%   $248.1284   $248.13   $248.15   $248.10  
  7 purchase totals = $896.21       $956.9062   $956.90   $956.95   $956.80