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 $154.98   12.261%   $173.9821   $173.98   $174.00   $174.00  
  Purchase #2 $231.39   10.484%   $255.6489   $255.65   $255.65   $255.60  
  Purchase #3 $61.40   8.794%   $66.7995   $66.80   $66.80   $66.80  
  Purchase #4 $39.98   8.606%   $43.4207   $43.42   $43.40   $43.40  
  Purchase #5 $184.41   8.607%   $200.2822   $200.28   $200.30   $200.30  
  Purchase #6 $209.31   8.775%   $227.677   $227.68   $227.70   $227.70  
  Purchase #7 $182.32   7.330%   $195.6841   $195.68   $195.70   $195.70  
  7 purchase totals = $1,063.79       $1,163.4945   $1,163.49   $1,163.55   $1,163.50