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 $144.47   6.562%   $153.9501   $153.95   $153.95   $154.00  
  Purchase #2 $33.31   6.168%   $35.3646   $35.36   $35.35   $35.40  
  Purchase #3 $200.33   12.415%   $225.201   $225.20   $225.20   $225.20  
  Purchase #4 $243.81   3.854%   $253.2064   $253.21   $253.20   $253.20  
  Purchase #5 $148.95   9.803%   $163.5516   $163.55   $163.55   $163.60  
  Purchase #6 $7.65   11.756%   $8.5493   $8.55   $8.55   $8.50  
  Purchase #7 $105.53   3.811%   $109.5517   $109.55   $109.55   $109.60  
  7 purchase totals = $884.05       $949.3747   $949.37   $949.35   $949.50