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 $64.76   8.522%   $70.2788   $70.28   $70.30   $70.30  
  Purchase #2 $226.72   13.484%   $257.2909   $257.29   $257.30   $257.30  
  Purchase #3 $153.71   9.373%   $168.1172   $168.12   $168.10   $168.10  
  Purchase #4 $67.79   7.763%   $73.0525   $73.05   $73.05   $73.10  
  Purchase #5 $18.49   10.803%   $20.4875   $20.49   $20.50   $20.50  
  Purchase #6 $202.39   12.366%   $227.4175   $227.42   $227.40   $227.40  
  Purchase #7 $170.33   3.684%   $176.605   $176.61   $176.60   $176.60  
  7 purchase totals = $904.19       $993.2494   $993.26   $993.25   $993.30