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 $238.60   8.106%   $257.9409   $257.94   $257.95   $257.90  
  Purchase #2 $217.85   5.563%   $229.969   $229.97   $229.95   $230.00  
  Purchase #3 $164.57   5.656%   $173.8781   $173.88   $173.90   $173.90  
  Purchase #4 $176.91   10.118%   $194.8098   $194.81   $194.80   $194.80  
  Purchase #5 $158.60   8.528%   $172.1254   $172.13   $172.15   $172.10  
  Purchase #6 $230.82   12.103%   $258.7561   $258.76   $258.75   $258.80  
  Purchase #7 $88.78   9.203%   $96.9504   $96.95   $96.95   $97.00  
  7 purchase totals = $1,276.13       $1,384.4297   $1,384.44   $1,384.45   $1,384.50