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 $247.79   13.474%   $281.1772   $281.18   $281.20   $281.20  
  Purchase #2 $75.47   9.447%   $82.5997   $82.60   $82.60   $82.60  
  Purchase #3 $114.78   10.367%   $126.6792   $126.68   $126.70   $126.70  
  Purchase #4 $6.41   5.465%   $6.7603   $6.76   $6.75   $6.80  
  Purchase #5 $146.87   10.811%   $162.7481   $162.75   $162.75   $162.70  
  Purchase #6 $216.69   4.222%   $225.8387   $225.84   $225.85   $225.80  
  Purchase #7 $158.41   8.372%   $171.6721   $171.67   $171.65   $171.70  
  7 purchase totals = $966.42       $1,057.4753   $1,057.48   $1,057.50   $1,057.50