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 $198.41   13.381%   $224.9592   $224.96   $224.95   $225.00  
  Purchase #2 $186.55   3.642%   $193.3442   $193.34   $193.35   $193.30  
  Purchase #3 $154.54   7.477%   $166.095   $166.10   $166.10   $166.10  
  Purchase #4 $85.87   11.174%   $95.4651   $95.47   $95.45   $95.50  
  Purchase #5 $146.97   11.764%   $164.2596   $164.26   $164.25   $164.30  
  Purchase #6 $95.53   9.703%   $104.7993   $104.80   $104.80   $104.80  
  Purchase #7 $176.82   9.339%   $193.3332   $193.33   $193.35   $193.30  
  7 purchase totals = $1,044.69       $1,142.2556   $1,142.26   $1,142.25   $1,142.30