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 $85.29   9.671%   $93.5384   $93.54   $93.55   $93.50  
  Purchase #2 $26.52   9.177%   $28.9537   $28.95   $28.95   $29.00  
  Purchase #3 $195.81   12.652%   $220.5839   $220.58   $220.60   $220.60  
  Purchase #4 $199.32   12.867%   $224.9665   $224.97   $224.95   $225.00  
  Purchase #5 $74.87   9.563%   $82.0298   $82.03   $82.05   $82.00  
  Purchase #6 $84.63   8.303%   $91.6568   $91.66   $91.65   $91.70  
  Purchase #7 $166.52   10.430%   $183.888   $183.89   $183.90   $183.90  
  7 purchase totals = $832.96       $925.6171   $925.62   $925.65   $925.70