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 $248.35   8.544%   $269.569   $269.57   $269.55   $269.60  
  Purchase #2 $230.33   4.184%   $239.967   $239.97   $239.95   $240.00  
  Purchase #3 $119.85   13.342%   $135.8404   $135.84   $135.85   $135.80  
  Purchase #4 $241.26   7.123%   $258.4449   $258.44   $258.45   $258.40  
  Purchase #5 $207.86   11.774%   $232.3334   $232.33   $232.35   $232.30  
  Purchase #6 $50.82   5.388%   $53.5582   $53.56   $53.55   $53.60  
  Purchase #7 $207.43   13.528%   $235.4911   $235.49   $235.50   $235.50  
  7 purchase totals = $1,305.90       $1,425.2040   $1,425.20   $1,425.20   $1,425.20