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 $156.45   8.232%   $169.329   $169.33   $169.35   $169.30  
  Purchase #2 $88.45   11.837%   $98.9198   $98.92   $98.90   $98.90  
  Purchase #3 $59.83   7.828%   $64.5135   $64.51   $64.50   $64.50  
  Purchase #4 $132.36   4.563%   $138.3996   $138.40   $138.40   $138.40  
  Purchase #5 $147.49   13.129%   $166.854   $166.85   $166.85   $166.90  
  Purchase #6 $171.91   10.834%   $190.5347   $190.53   $190.55   $190.50  
  Purchase #7 $111.33   3.625%   $115.3657   $115.37   $115.35   $115.40  
  7 purchase totals = $867.82       $943.9163   $943.91   $943.90   $943.90