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 $113.55   12.661%   $127.9266   $127.93   $127.95   $127.90  
  Purchase #2 $22.73   9.113%   $24.8014   $24.80   $24.80   $24.80  
  Purchase #3 $178.40   6.341%   $189.7123   $189.71   $189.70   $189.70  
  Purchase #4 $69.57   10.512%   $76.8832   $76.88   $76.90   $76.90  
  Purchase #5 $41.26   13.609%   $46.8751   $46.88   $46.90   $46.90  
  Purchase #6 $150.30   8.659%   $163.3145   $163.31   $163.30   $163.30  
  Purchase #7 $121.59   8.765%   $132.2474   $132.25   $132.25   $132.20  
  7 purchase totals = $697.40       $761.7605   $761.76   $761.80   $761.70