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 $109.69   8.168%   $118.6495   $118.65   $118.65   $118.60  
  Purchase #2 $13.71   12.155%   $15.3765   $15.38   $15.40   $15.40  
  Purchase #3 $170.35   9.218%   $186.0529   $186.05   $186.05   $186.10  
  Purchase #4 $247.83   10.389%   $273.5771   $273.58   $273.60   $273.60  
  Purchase #5 $24.32   8.722%   $26.4412   $26.44   $26.45   $26.40  
  Purchase #6 $195.35   12.169%   $219.1221   $219.12   $219.10   $219.10  
  Purchase #7 $215.54   11.583%   $240.506   $240.51   $240.50   $240.50  
  7 purchase totals = $976.79       $1,079.7253   $1,079.73   $1,079.75   $1,079.70