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 $201.38   8.528%   $218.5537   $218.55   $218.55   $218.60  
  Purchase #2 $52.65   3.663%   $54.5786   $54.58   $54.60   $54.60  
  Purchase #3 $244.61   6.412%   $260.2944   $260.29   $260.30   $260.30  
  Purchase #4 $125.53   6.165%   $133.2689   $133.27   $133.25   $133.30  
  Purchase #5 $109.48   9.153%   $119.5007   $119.50   $119.50   $119.50  
  Purchase #6 $241.66   11.170%   $268.6534   $268.65   $268.65   $268.70  
  Purchase #7 $60.36   7.396%   $64.8242   $64.82   $64.80   $64.80  
  7 purchase totals = $1,035.67       $1,119.6739   $1,119.66   $1,119.65   $1,119.80