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 $244.69   5.451%   $258.0281   $258.03   $258.05   $258.00  
  Purchase #2 $122.57   10.837%   $135.8529   $135.85   $135.85   $135.90  
  Purchase #3 $206.46   5.476%   $217.7657   $217.77   $217.75   $217.80  
  Purchase #4 $223.59   11.606%   $249.5399   $249.54   $249.55   $249.50  
  Purchase #5 $152.28   9.126%   $166.1771   $166.18   $166.20   $166.20  
  Purchase #6 $202.33   11.486%   $225.5696   $225.57   $225.55   $225.60  
  Purchase #7 $220.42   8.450%   $239.0455   $239.05   $239.05   $239.00  
  7 purchase totals = $1,372.34       $1,491.9788   $1,491.99   $1,492.00   $1,492.00