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 $211.48   11.857%   $236.5552   $236.56   $236.55   $236.60  
  Purchase #2 $166.67   4.669%   $174.4518   $174.45   $174.45   $174.50  
  Purchase #3 $105.34   7.363%   $113.0962   $113.10   $113.10   $113.10  
  Purchase #4 $21.77   4.537%   $22.7577   $22.76   $22.75   $22.80  
  Purchase #5 $244.39   9.844%   $268.4478   $268.45   $268.45   $268.40  
  Purchase #6 $153.29   11.452%   $170.8448   $170.84   $170.85   $170.80  
  Purchase #7 $42.97   12.833%   $48.4843   $48.48   $48.50   $48.50  
  7 purchase totals = $945.91       $1,034.6378   $1,034.64   $1,034.65   $1,034.70