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 $23.97   8.580%   $26.0266   $26.03   $26.05   $26.00  
  Purchase #2 $163.27   5.581%   $172.3821   $172.38   $172.40   $172.40  
  Purchase #3 $195.92   12.429%   $220.2709   $220.27   $220.25   $220.30  
  Purchase #4 $59.31   3.527%   $61.4019   $61.40   $61.40   $61.40  
  Purchase #5 $70.82   9.508%   $77.5536   $77.55   $77.55   $77.60  
  Purchase #6 $204.72   5.854%   $216.7043   $216.70   $216.70   $216.70  
  Purchase #7 $64.47   7.467%   $69.284   $69.28   $69.30   $69.30  
  7 purchase totals = $782.48       $843.6234   $843.61   $843.65   $843.70