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 $214.97   9.814%   $236.0672   $236.07   $236.05   $236.10  
  Purchase #2 $210.81   11.695%   $235.4642   $235.46   $235.45   $235.50  
  Purchase #3 $78.82   11.487%   $87.8741   $87.87   $87.85   $87.90  
  Purchase #4 $76.45   10.126%   $84.1913   $84.19   $84.20   $84.20  
  Purchase #5 $153.46   12.254%   $172.265   $172.27   $172.25   $172.30  
  Purchase #6 $42.41   9.772%   $46.5543   $46.55   $46.55   $46.60  
  Purchase #7 $104.38   9.360%   $114.15   $114.15   $114.15   $114.20  
  7 purchase totals = $881.30       $976.5661   $976.56   $976.50   $976.80