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 $226.48   9.171%   $247.2505   $247.25   $247.25   $247.30  
  Purchase #2 $184.98   8.638%   $200.9586   $200.96   $200.95   $201.00  
  Purchase #3 $44.33   5.552%   $46.7912   $46.79   $46.80   $46.80  
  Purchase #4 $32.88   3.213%   $33.9364   $33.94   $33.95   $33.90  
  Purchase #5 $148.77   3.178%   $153.4979   $153.50   $153.50   $153.50  
  Purchase #6 $15.35   7.292%   $16.4693   $16.47   $16.45   $16.50  
  Purchase #7 $62.93   9.762%   $69.0732   $69.07   $69.05   $69.10  
  7 purchase totals = $715.72       $767.9771   $767.98   $767.95   $768.10