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 $23.66   13.692%   $26.8995   $26.90   $26.90   $26.90  
  Purchase #2 $117.45   6.114%   $124.6309   $124.63   $124.65   $124.60  
  Purchase #3 $84.27   8.281%   $91.2484   $91.25   $91.25   $91.20  
  Purchase #4 $147.96   10.706%   $163.8006   $163.80   $163.80   $163.80  
  Purchase #5 $150.36   3.493%   $155.6121   $155.61   $155.60   $155.60  
  Purchase #6 $21.38   7.319%   $22.9448   $22.94   $22.95   $22.90  
  Purchase #7 $217.64   10.723%   $240.9775   $240.98   $241.00   $241.00  
  7 purchase totals = $762.72       $826.1138   $826.11   $826.15   $826.00