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 $229.60   11.671%   $256.3966   $256.40   $256.40   $256.40  
  Purchase #2 $176.25   10.297%   $194.3985   $194.40   $194.40   $194.40  
  Purchase #3 $139.76   10.713%   $154.7325   $154.73   $154.75   $154.70  
  Purchase #4 $166.97   4.838%   $175.048   $175.05   $175.05   $175.00  
  Purchase #5 $212.74   9.198%   $232.3078   $232.31   $232.30   $232.30  
  Purchase #6 $22.55   11.848%   $25.2217   $25.22   $25.20   $25.20  
  Purchase #7 $44.25   6.790%   $47.2546   $47.25   $47.25   $47.30  
  7 purchase totals = $992.12       $1,085.3597   $1,085.36   $1,085.35   $1,085.30