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 $35.98   5.620%   $38.0021   $38.00   $38.00   $38.00  
  Purchase #2 $220.35   7.534%   $236.9512   $236.95   $236.95   $237.00  
  Purchase #3 $23.82   13.226%   $26.9704   $26.97   $26.95   $27.00  
  Purchase #4 $66.56   7.771%   $71.7324   $71.73   $71.75   $71.70  
  Purchase #5 $92.60   11.367%   $103.1258   $103.13   $103.15   $103.10  
  Purchase #6 $240.33   4.279%   $250.6137   $250.61   $250.60   $250.60  
  Purchase #7 $95.30   12.852%   $107.548   $107.55   $107.55   $107.50  
  7 purchase totals = $774.94       $834.9436   $834.94   $834.95   $834.90