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 $85.29   11.341%   $94.9627   $94.96   $94.95   $95.00  
  Purchase #2 $63.94   3.211%   $65.9931   $65.99   $66.00   $66.00  
  Purchase #3 $158.57   7.730%   $170.8275   $170.83   $170.85   $170.80  
  Purchase #4 $113.90   3.381%   $117.751   $117.75   $117.75   $117.80  
  Purchase #5 $120.37   13.830%   $137.0172   $137.02   $137.00   $137.00  
  Purchase #6 $204.35   10.726%   $226.2686   $226.27   $226.25   $226.30  
  Purchase #7 $103.63   6.725%   $110.5991   $110.60   $110.60   $110.60  
  7 purchase totals = $850.05       $923.4192   $923.42   $923.40   $923.50