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 $228.84   6.621%   $243.9915   $243.99   $244.00   $244.00  
  Purchase #2 $142.35   13.439%   $161.4804   $161.48   $161.50   $161.50  
  Purchase #3 $248.53   7.565%   $267.3313   $267.33   $267.35   $267.30  
  Purchase #4 $229.78   4.540%   $240.212   $240.21   $240.20   $240.20  
  Purchase #5 $247.39   4.562%   $258.6759   $258.68   $258.70   $258.70  
  Purchase #6 $164.76   12.692%   $185.6713   $185.67   $185.65   $185.70  
  Purchase #7 $99.76   9.151%   $108.889   $108.89   $108.90   $108.90  
  7 purchase totals = $1,361.41       $1,466.2514   $1,466.25   $1,466.30   $1,466.30