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 $246.68   8.496%   $267.6379   $267.64   $267.65   $267.60  
  Purchase #2 $54.98   10.111%   $60.539   $60.54   $60.55   $60.50  
  Purchase #3 $22.75   8.413%   $24.664   $24.66   $24.65   $24.70  
  Purchase #4 $204.86   12.475%   $230.4163   $230.42   $230.40   $230.40  
  Purchase #5 $54.78   5.703%   $57.9041   $57.90   $57.90   $57.90  
  Purchase #6 $11.86   12.227%   $13.3101   $13.31   $13.30   $13.30  
  Purchase #7 $66.87   10.206%   $73.6948   $73.69   $73.70   $73.70  
  7 purchase totals = $662.78       $728.1662   $728.16   $728.15   $728.10