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 $142.41   6.414%   $151.5442   $151.54   $151.55   $151.50  
  Purchase #2 $206.43   12.593%   $232.4257   $232.43   $232.45   $232.40  
  Purchase #3 $31.68   5.826%   $33.5257   $33.53   $33.55   $33.50  
  Purchase #4 $240.77   7.744%   $259.4152   $259.42   $259.40   $259.40  
  Purchase #5 $227.83   10.549%   $251.8638   $251.86   $251.85   $251.90  
  Purchase #6 $241.80   8.781%   $263.0325   $263.03   $263.05   $263.00  
  Purchase #7 $66.76   5.535%   $70.4552   $70.46   $70.45   $70.50  
  7 purchase totals = $1,157.68       $1,262.2623   $1,262.27   $1,262.30   $1,262.20