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 $245.43   7.550%   $263.96   $263.96   $263.95   $264.00  
  Purchase #2 $10.36   8.290%   $11.2188   $11.22   $11.20   $11.20  
  Purchase #3 $121.33   7.350%   $130.2478   $130.25   $130.25   $130.20  
  Purchase #4 $60.66   9.290%   $66.2953   $66.30   $66.30   $66.30  
  Purchase #5 $218.64   10.660%   $241.947   $241.95   $241.95   $241.90  
  Purchase #6 $26.47   7.820%   $28.54   $28.54   $28.55   $28.50  
  Purchase #7 $32.46   7.686%   $34.9549   $34.95   $34.95   $35.00  
  7 purchase totals = $715.35       $777.1638   $777.17   $777.15   $777.10