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 $242.71   10.120%   $267.2723   $267.27   $267.25   $267.30  
  Purchase #2 $61.81   6.462%   $65.8042   $65.80   $65.80   $65.80  
  Purchase #3 $235.73   13.793%   $268.2442   $268.24   $268.25   $268.20  
  Purchase #4 $201.64   11.756%   $225.3448   $225.34   $225.35   $225.30  
  Purchase #5 $215.41   9.181%   $235.1868   $235.19   $235.20   $235.20  
  Purchase #6 $15.55   4.869%   $16.3071   $16.31   $16.30   $16.30  
  Purchase #7 $54.42   5.601%   $57.4681   $57.47   $57.45   $57.50  
  7 purchase totals = $1,027.27       $1,135.6275   $1,135.62   $1,135.60   $1,135.60