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 $67.77   13.555%   $76.9562   $76.96   $76.95   $77.00  
  Purchase #2 $196.93   9.761%   $216.1523   $216.15   $216.15   $216.20  
  Purchase #3 $211.57   7.751%   $227.9688   $227.97   $227.95   $228.00  
  Purchase #4 $20.82   13.811%   $23.6955   $23.70   $23.70   $23.70  
  Purchase #5 $180.77   10.668%   $200.0545   $200.05   $200.05   $200.10  
  Purchase #6 $61.78   7.545%   $66.4413   $66.44   $66.45   $66.40  
  Purchase #7 $18.27   4.127%   $19.024   $19.02   $19.00   $19.00  
  7 purchase totals = $757.91       $830.2926   $830.29   $830.25   $830.40