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 $188.66   8.513%   $204.7206   $204.72   $204.70   $204.70  
  Purchase #2 $55.40   11.211%   $61.6109   $61.61   $61.60   $61.60  
  Purchase #3 $197.28   12.195%   $221.3383   $221.34   $221.35   $221.30  
  Purchase #4 $40.92   5.491%   $43.1669   $43.17   $43.15   $43.20  
  Purchase #5 $144.41   9.848%   $158.6315   $158.63   $158.65   $158.60  
  Purchase #6 $59.85   7.107%   $64.1035   $64.10   $64.10   $64.10  
  Purchase #7 $5.28   8.770%   $5.7431   $5.74   $5.75   $5.70  
  7 purchase totals = $691.80       $759.3148   $759.31   $759.30   $759.20