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 $246.79   10.466%   $272.619   $272.62   $272.60   $272.60  
  Purchase #2 $222.59   6.742%   $237.597   $237.60   $237.60   $237.60  
  Purchase #3 $120.48   13.308%   $136.5135   $136.51   $136.50   $136.50  
  Purchase #4 $167.57   5.485%   $176.7612   $176.76   $176.75   $176.80  
  Purchase #5 $202.40   4.625%   $211.761   $211.76   $211.75   $211.80  
  Purchase #6 $167.50   5.200%   $176.21   $176.21   $176.20   $176.20  
  Purchase #7 $69.64   9.315%   $76.127   $76.13   $76.15   $76.10  
  7 purchase totals = $1,196.97       $1,287.5887   $1,287.59   $1,287.55   $1,287.60