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 $69.29   5.546%   $73.1328   $73.13   $73.15   $73.10  
  Purchase #2 $226.83   11.622%   $253.1922   $253.19   $253.20   $253.20  
  Purchase #3 $112.44   10.280%   $123.9988   $124.00   $124.00   $124.00  
  Purchase #4 $118.42   7.590%   $127.4081   $127.41   $127.40   $127.40  
  Purchase #5 $10.87   5.873%   $11.5084   $11.51   $11.50   $11.50  
  Purchase #6 $127.94   7.703%   $137.7952   $137.80   $137.80   $137.80  
  Purchase #7 $181.29   9.670%   $198.8207   $198.82   $198.80   $198.80  
  7 purchase totals = $847.08       $925.8562   $925.86   $925.85   $925.80