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 $240.64   11.242%   $267.6927   $267.69   $267.70   $267.70  
  Purchase #2 $29.84   4.587%   $31.2088   $31.21   $31.20   $31.20  
  Purchase #3 $26.51   10.658%   $29.3354   $29.34   $29.35   $29.30  
  Purchase #4 $134.30   8.315%   $145.467   $145.47   $145.45   $145.50  
  Purchase #5 $104.63   10.534%   $115.6517   $115.65   $115.65   $115.70  
  Purchase #6 $235.82   11.396%   $262.694   $262.69   $262.70   $262.70  
  Purchase #7 $194.85   13.472%   $221.1002   $221.10   $221.10   $221.10  
  7 purchase totals = $966.59       $1,073.1498   $1,073.15   $1,073.15   $1,073.20