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 $208.60   7.732%   $224.729   $224.73   $224.75   $224.70  
  Purchase #2 $102.59   13.392%   $116.3289   $116.33   $116.35   $116.30  
  Purchase #3 $146.40   4.350%   $152.7684   $152.77   $152.75   $152.80  
  Purchase #4 $227.57   6.286%   $241.8751   $241.88   $241.90   $241.90  
  Purchase #5 $226.82   13.854%   $258.2436   $258.24   $258.25   $258.20  
  Purchase #6 $68.57   13.169%   $77.6   $77.60   $77.60   $77.60  
  Purchase #7 $90.31   8.543%   $98.0252   $98.03   $98.05   $98.00  
  7 purchase totals = $1,070.86       $1,169.5702   $1,169.58   $1,169.65   $1,169.50