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 $23.78   9.592%   $26.061   $26.06   $26.05   $26.10  
  Purchase #2 $91.78   8.808%   $99.864   $99.86   $99.85   $99.90  
  Purchase #3 $228.25   8.215%   $247.0007   $247.00   $247.00   $247.00  
  Purchase #4 $65.79   8.325%   $71.267   $71.27   $71.25   $71.30  
  Purchase #5 $76.54   4.281%   $79.8167   $79.82   $79.80   $79.80  
  Purchase #6 $236.62   11.490%   $263.8076   $263.81   $263.80   $263.80  
  Purchase #7 $66.71   12.307%   $74.92   $74.92   $74.90   $74.90  
  7 purchase totals = $789.47       $862.7370   $862.74   $862.65   $862.80