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 $97.62   8.685%   $106.0983   $106.10   $106.10   $106.10  
  Purchase #2 $196.48   5.521%   $207.3277   $207.33   $207.35   $207.30  
  Purchase #3 $233.37   11.390%   $259.9508   $259.95   $259.95   $260.00  
  Purchase #4 $64.76   9.374%   $70.8306   $70.83   $70.85   $70.80  
  Purchase #5 $151.91   11.411%   $169.2445   $169.24   $169.25   $169.20  
  Purchase #6 $141.99   3.475%   $146.9242   $146.92   $146.90   $146.90  
  Purchase #7 $9.26   3.550%   $9.5887   $9.59   $9.60   $9.60  
  7 purchase totals = $895.39       $969.9648   $969.96   $970.00   $969.90