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 $142.91   5.666%   $151.0073   $151.01   $151.00   $151.00  
  Purchase #2 $68.71   4.347%   $71.6968   $71.70   $71.70   $71.70  
  Purchase #3 $78.78   10.428%   $86.9952   $87.00   $87.00   $87.00  
  Purchase #4 $14.74   8.761%   $16.0314   $16.03   $16.05   $16.00  
  Purchase #5 $45.40   4.706%   $47.5365   $47.54   $47.55   $47.50  
  Purchase #6 $168.59   6.689%   $179.867   $179.87   $179.85   $179.90  
  Purchase #7 $164.63   12.649%   $185.454   $185.45   $185.45   $185.50  
  7 purchase totals = $683.76       $738.5882   $738.60   $738.60   $738.60