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 $66.82   8.673%   $72.6153   $72.62   $72.60   $72.60  
  Purchase #2 $206.59   5.403%   $217.7521   $217.75   $217.75   $217.80  
  Purchase #3 $33.92   5.205%   $35.6855   $35.69   $35.70   $35.70  
  Purchase #4 $141.32   6.542%   $150.5652   $150.57   $150.55   $150.60  
  Purchase #5 $217.29   9.203%   $237.2872   $237.29   $237.30   $237.30  
  Purchase #6 $106.49   3.869%   $110.6101   $110.61   $110.60   $110.60  
  Purchase #7 $10.55   8.813%   $11.4798   $11.48   $11.50   $11.50  
  7 purchase totals = $782.98       $835.9952   $836.01   $836.00   $836.10