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 $201.93   13.861%   $229.9195   $229.92   $229.90   $229.90  
  Purchase #2 $85.39   12.382%   $95.963   $95.96   $95.95   $96.00  
  Purchase #3 $155.45   13.495%   $176.428   $176.43   $176.45   $176.40  
  Purchase #4 $242.68   3.447%   $251.0452   $251.05   $251.05   $251.00  
  Purchase #5 $148.65   6.250%   $157.9406   $157.94   $157.95   $157.90  
  Purchase #6 $168.43   4.814%   $176.5382   $176.54   $176.55   $176.50  
  Purchase #7 $186.68   3.106%   $192.4783   $192.48   $192.50   $192.50  
  7 purchase totals = $1,189.21       $1,280.3128   $1,280.32   $1,280.35   $1,280.20