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 $23.94   8.505%   $25.9761   $25.98   $26.00   $26.00  
  Purchase #2 $5.31   13.331%   $6.0179   $6.02   $6.00   $6.00  
  Purchase #3 $180.92   11.506%   $201.7367   $201.74   $201.75   $201.70  
  Purchase #4 $75.90   4.820%   $79.5584   $79.56   $79.55   $79.60  
  Purchase #5 $74.80   12.833%   $84.3991   $84.40   $84.40   $84.40  
  Purchase #6 $174.41   4.540%   $182.3282   $182.33   $182.35   $182.30  
  Purchase #7 $119.90   13.723%   $136.3539   $136.35   $136.35   $136.40  
  7 purchase totals = $655.18       $716.3703   $716.38   $716.40   $716.40