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 $49.83   4.827%   $52.2353   $52.24   $52.25   $52.20  
  Purchase #2 $98.55   6.199%   $104.6591   $104.66   $104.65   $104.70  
  Purchase #3 $149.85   3.687%   $155.375   $155.38   $155.40   $155.40  
  Purchase #4 $214.76   3.827%   $222.9789   $222.98   $223.00   $223.00  
  Purchase #5 $250.60   10.177%   $276.1036   $276.10   $276.10   $276.10  
  Purchase #6 $239.56   3.461%   $247.8512   $247.85   $247.85   $247.90  
  Purchase #7 $24.29   6.664%   $25.9087   $25.91   $25.90   $25.90  
  7 purchase totals = $1,027.44       $1,085.1118   $1,085.12   $1,085.15   $1,085.20