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 $45.82   9.192%   $50.0318   $50.03   $50.05   $50.00  
  Purchase #2 $86.86   9.713%   $95.2967   $95.30   $95.30   $95.30  
  Purchase #3 $174.37   13.863%   $198.5429   $198.54   $198.55   $198.50  
  Purchase #4 $239.79   12.255%   $269.1763   $269.18   $269.20   $269.20  
  Purchase #5 $11.93   4.106%   $12.4198   $12.42   $12.40   $12.40  
  Purchase #6 $17.25   7.580%   $18.5576   $18.56   $18.55   $18.60  
  Purchase #7 $119.95   10.226%   $132.2161   $132.22   $132.20   $132.20  
  7 purchase totals = $695.97       $776.2412   $776.25   $776.25   $776.20