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 $53.33   11.857%   $59.6533   $59.65   $59.65   $59.70  
  Purchase #2 $105.83   11.187%   $117.6692   $117.67   $117.65   $117.70  
  Purchase #3 $171.77   10.754%   $190.2421   $190.24   $190.25   $190.20  
  Purchase #4 $211.25   13.807%   $240.4173   $240.42   $240.40   $240.40  
  Purchase #5 $5.98   3.423%   $6.1847   $6.18   $6.20   $6.20  
  Purchase #6 $196.53   10.311%   $216.7942   $216.79   $216.80   $216.80  
  Purchase #7 $83.63   10.254%   $92.2054   $92.21   $92.20   $92.20  
  7 purchase totals = $828.32       $923.1662   $923.16   $923.15   $923.20