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 $64.58   4.698%   $67.614   $67.61   $67.60   $67.60  
  Purchase #2 $65.47   10.772%   $72.5224   $72.52   $72.50   $72.50  
  Purchase #3 $119.88   10.674%   $132.676   $132.68   $132.70   $132.70  
  Purchase #4 $47.77   8.517%   $51.8386   $51.84   $51.85   $51.80  
  Purchase #5 $97.68   8.639%   $106.1186   $106.12   $106.10   $106.10  
  Purchase #6 $165.89   6.348%   $176.4207   $176.42   $176.40   $176.40  
  Purchase #7 $154.48   4.797%   $161.8904   $161.89   $161.90   $161.90  
  7 purchase totals = $715.75       $769.0807   $769.08   $769.05   $769.00