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 $155.76   6.781%   $166.3221   $166.32   $166.30   $166.30  
  Purchase #2 $239.27   7.534%   $257.2966   $257.30   $257.30   $257.30  
  Purchase #3 $222.69   6.324%   $236.7729   $236.77   $236.75   $236.80  
  Purchase #4 $103.59   3.342%   $107.052   $107.05   $107.05   $107.10  
  Purchase #5 $57.47   13.146%   $65.025   $65.03   $65.05   $65.00  
  Purchase #6 $139.98   8.739%   $152.2129   $152.21   $152.20   $152.20  
  Purchase #7 $142.26   12.326%   $159.795   $159.80   $159.80   $159.80  
  7 purchase totals = $1,061.02       $1,144.4765   $1,144.48   $1,144.45   $1,144.50