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 $59.48   5.871%   $62.9721   $62.97   $62.95   $63.00  
  Purchase #2 $163.62   8.575%   $177.6504   $177.65   $177.65   $177.70  
  Purchase #3 $94.73   6.413%   $100.805   $100.81   $100.80   $100.80  
  Purchase #4 $116.37   8.517%   $126.2812   $126.28   $126.30   $126.30  
  Purchase #5 $116.69   4.452%   $121.885   $121.89   $121.90   $121.90  
  Purchase #6 $216.34   3.874%   $224.721   $224.72   $224.70   $224.70  
  Purchase #7 $23.25   6.246%   $24.7022   $24.70   $24.70   $24.70  
  7 purchase totals = $790.48       $839.0169   $839.02   $839.00   $839.10