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 $178.46   4.602%   $186.6727   $186.67   $186.65   $186.70  
  Purchase #2 $181.65   8.283%   $196.6961   $196.70   $196.70   $196.70  
  Purchase #3 $141.81   12.398%   $159.3916   $159.39   $159.40   $159.40  
  Purchase #4 $197.48   5.799%   $208.9319   $208.93   $208.95   $208.90  
  Purchase #5 $131.51   11.337%   $146.4193   $146.42   $146.40   $146.40  
  Purchase #6 $26.41   13.367%   $29.9402   $29.94   $29.95   $29.90  
  Purchase #7 $85.46   11.318%   $95.1324   $95.13   $95.15   $95.10  
  7 purchase totals = $942.78       $1,023.1842   $1,023.18   $1,023.20   $1,023.10