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 $62.78   10.626%   $69.451   $69.45   $69.45   $69.50  
  Purchase #2 $61.58   11.234%   $68.4979   $68.50   $68.50   $68.50  
  Purchase #3 $30.53   8.783%   $33.2114   $33.21   $33.20   $33.20  
  Purchase #4 $140.75   7.815%   $151.7496   $151.75   $151.75   $151.70  
  Purchase #5 $243.95   8.821%   $265.4688   $265.47   $265.45   $265.50  
  Purchase #6 $36.80   7.521%   $39.5677   $39.57   $39.55   $39.60  
  Purchase #7 $176.63   9.607%   $193.5988   $193.60   $193.60   $193.60  
  7 purchase totals = $753.02       $821.5452   $821.55   $821.50   $821.60