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 $226.73   12.326%   $254.6767   $254.68   $254.70   $254.70  
  Purchase #2 $118.36   7.208%   $126.8914   $126.89   $126.90   $126.90  
  Purchase #3 $19.59   9.704%   $21.491   $21.49   $21.50   $21.50  
  Purchase #4 $162.63   5.772%   $172.017   $172.02   $172.00   $172.00  
  Purchase #5 $240.92   9.438%   $263.658   $263.66   $263.65   $263.70  
  Purchase #6 $243.51   4.438%   $254.317   $254.32   $254.30   $254.30  
  Purchase #7 $82.65   9.677%   $90.648   $90.65   $90.65   $90.60  
  7 purchase totals = $1,094.39       $1,183.6991   $1,183.71   $1,183.70   $1,183.70