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 $153.87   3.459%   $159.1924   $159.19   $159.20   $159.20  
  Purchase #2 $65.62   8.732%   $71.3499   $71.35   $71.35   $71.30  
  Purchase #3 $115.37   3.597%   $119.5199   $119.52   $119.50   $119.50  
  Purchase #4 $53.75   5.746%   $56.8385   $56.84   $56.85   $56.80  
  Purchase #5 $101.86   9.585%   $111.6233   $111.62   $111.60   $111.60  
  Purchase #6 $203.87   3.133%   $210.2572   $210.26   $210.25   $210.30  
  Purchase #7 $166.98   11.858%   $186.7805   $186.78   $186.80   $186.80  
  7 purchase totals = $861.32       $915.5617   $915.56   $915.55   $915.50