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 $216.95   3.323%   $224.1592   $224.16   $224.15   $224.20  
  Purchase #2 $25.56   5.166%   $26.8804   $26.88   $26.90   $26.90  
  Purchase #3 $202.46   3.315%   $209.1715   $209.17   $209.15   $209.20  
  Purchase #4 $184.32   5.639%   $194.7138   $194.71   $194.70   $194.70  
  Purchase #5 $231.62   5.453%   $244.2502   $244.25   $244.25   $244.30  
  Purchase #6 $227.84   13.826%   $259.3412   $259.34   $259.35   $259.30  
  Purchase #7 $107.95   4.689%   $113.0118   $113.01   $113.00   $113.00  
  7 purchase totals = $1,196.70       $1,271.5281   $1,271.52   $1,271.50   $1,271.60