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 $244.27   6.822%   $260.9341   $260.93   $260.95   $260.90  
  Purchase #2 $200.78   7.853%   $216.5473   $216.55   $216.55   $216.50  
  Purchase #3 $127.73   5.414%   $134.6453   $134.65   $134.65   $134.60  
  Purchase #4 $156.90   3.198%   $161.9177   $161.92   $161.90   $161.90  
  Purchase #5 $144.82   7.566%   $155.7771   $155.78   $155.80   $155.80  
  Purchase #6 $151.77   8.364%   $164.464   $164.46   $164.45   $164.50  
  Purchase #7 $219.39   4.699%   $229.6991   $229.70   $229.70   $229.70  
  7 purchase totals = $1,245.66       $1,323.9846   $1,323.99   $1,324.00   $1,323.90