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 $54.84   10.647%   $60.6788   $60.68   $60.70   $60.70  
  Purchase #2 $139.39   13.692%   $158.4753   $158.48   $158.50   $158.50  
  Purchase #3 $120.30   3.451%   $124.4516   $124.45   $124.45   $124.50  
  Purchase #4 $231.90   13.265%   $262.6615   $262.66   $262.65   $262.70  
  Purchase #5 $8.70   6.494%   $9.265   $9.27   $9.25   $9.30  
  Purchase #6 $49.32   11.199%   $54.8433   $54.84   $54.85   $54.80  
  Purchase #7 $250.42   9.669%   $274.6331   $274.63   $274.65   $274.60  
  7 purchase totals = $854.87       $945.0086   $945.01   $945.05   $945.10