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 $194.76   12.462%   $219.031   $219.03   $219.05   $219.00  
  Purchase #2 $67.94   11.458%   $75.7246   $75.72   $75.70   $75.70  
  Purchase #3 $62.47   3.384%   $64.584   $64.58   $64.60   $64.60  
  Purchase #4 $55.55   7.111%   $59.5002   $59.50   $59.50   $59.50  
  Purchase #5 $97.46   12.110%   $109.2624   $109.26   $109.25   $109.30  
  Purchase #6 $163.87   7.736%   $176.547   $176.55   $176.55   $176.50  
  Purchase #7 $118.64   9.354%   $129.7376   $129.74   $129.75   $129.70  
  7 purchase totals = $760.69       $834.3868   $834.38   $834.40   $834.30