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 $112.68   3.151%   $116.2305   $116.23   $116.25   $116.20  
  Purchase #2 $173.99   11.606%   $194.1833   $194.18   $194.20   $194.20  
  Purchase #3 $124.49   3.824%   $129.2505   $129.25   $129.25   $129.30  
  Purchase #4 $196.83   10.603%   $217.6999   $217.70   $217.70   $217.70  
  Purchase #5 $121.78   4.676%   $127.4744   $127.47   $127.45   $127.50  
  Purchase #6 $23.52   10.527%   $25.996   $26.00   $26.00   $26.00  
  Purchase #7 $21.96   4.216%   $22.8858   $22.89   $22.90   $22.90  
  7 purchase totals = $775.25       $833.7204   $833.72   $833.75   $833.80