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 $94.93   3.808%   $98.5449   $98.54   $98.55   $98.50  
  Purchase #2 $10.80   8.551%   $11.7235   $11.72   $11.70   $11.70  
  Purchase #3 $231.63   4.138%   $241.2148   $241.21   $241.20   $241.20  
  Purchase #4 $118.85   12.183%   $133.3295   $133.33   $133.35   $133.30  
  Purchase #5 $53.49   13.228%   $60.5657   $60.57   $60.55   $60.60  
  Purchase #6 $158.34   10.373%   $174.7646   $174.76   $174.75   $174.80  
  Purchase #7 $40.97   4.264%   $42.717   $42.72   $42.70   $42.70  
  7 purchase totals = $709.01       $762.8600   $762.85   $762.80   $762.80