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 $194.94   5.583%   $205.8235   $205.82   $205.80   $205.80  
  Purchase #2 $249.32   13.736%   $283.5666   $283.57   $283.55   $283.60  
  Purchase #3 $111.26   7.525%   $119.6323   $119.63   $119.65   $119.60  
  Purchase #4 $232.94   12.164%   $261.2748   $261.27   $261.25   $261.30  
  Purchase #5 $244.27   6.242%   $259.5173   $259.52   $259.50   $259.50  
  Purchase #6 $58.25   12.168%   $65.3379   $65.34   $65.35   $65.30  
  Purchase #7 $131.50   7.127%   $140.872   $140.87   $140.85   $140.90  
  7 purchase totals = $1,222.48       $1,336.0244   $1,336.02   $1,335.95   $1,336.00