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 $109.36   8.239%   $118.3702   $118.37   $118.35   $118.40  
  Purchase #2 $183.67   7.178%   $196.8538   $196.85   $196.85   $196.90  
  Purchase #3 $16.52   12.296%   $18.5513   $18.55   $18.55   $18.60  
  Purchase #4 $53.48   12.157%   $59.9816   $59.98   $60.00   $60.00  
  Purchase #5 $154.84   8.434%   $167.8992   $167.90   $167.90   $167.90  
  Purchase #6 $195.67   9.584%   $214.423   $214.42   $214.40   $214.40  
  Purchase #7 $17.80   5.442%   $18.7687   $18.77   $18.75   $18.80  
  7 purchase totals = $731.34       $794.8478   $794.84   $794.80   $795.00