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 $126.34   7.181%   $135.4125   $135.41   $135.40   $135.40  
  Purchase #2 $160.59   7.300%   $172.3131   $172.31   $172.30   $172.30  
  Purchase #3 $36.88   9.227%   $40.2829   $40.28   $40.30   $40.30  
  Purchase #4 $121.90   13.329%   $138.1481   $138.15   $138.15   $138.10  
  Purchase #5 $209.76   3.480%   $217.0596   $217.06   $217.05   $217.10  
  Purchase #6 $182.35   8.631%   $198.0886   $198.09   $198.10   $198.10  
  Purchase #7 $229.31   3.476%   $237.2808   $237.28   $237.30   $237.30  
  7 purchase totals = $1,067.13       $1,138.5856   $1,138.58   $1,138.60   $1,138.60