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 $84.83   11.612%   $94.6805   $94.68   $94.70   $94.70  
  Purchase #2 $90.68   13.626%   $103.0361   $103.04   $103.05   $103.00  
  Purchase #3 $60.50   7.607%   $65.1022   $65.10   $65.10   $65.10  
  Purchase #4 $35.90   9.580%   $39.3392   $39.34   $39.35   $39.30  
  Purchase #5 $230.32   10.845%   $255.2982   $255.30   $255.30   $255.30  
  Purchase #6 $117.50   10.348%   $129.6589   $129.66   $129.65   $129.70  
  Purchase #7 $163.42   13.148%   $184.9065   $184.91   $184.90   $184.90  
  7 purchase totals = $783.15       $872.0216   $872.03   $872.05   $872.00