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 $224.32   13.588%   $254.8006   $254.80   $254.80   $254.80  
  Purchase #2 $244.43   3.836%   $253.8063   $253.81   $253.80   $253.80  
  Purchase #3 $151.25   12.309%   $169.8674   $169.87   $169.85   $169.90  
  Purchase #4 $136.72   11.606%   $152.5877   $152.59   $152.60   $152.60  
  Purchase #5 $199.53   7.515%   $214.5247   $214.52   $214.50   $214.50  
  Purchase #6 $102.79   13.646%   $116.8167   $116.82   $116.80   $116.80  
  Purchase #7 $92.95   3.309%   $96.0257   $96.03   $96.05   $96.00  
  7 purchase totals = $1,151.99       $1,258.4291   $1,258.44   $1,258.40   $1,258.40