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 $219.89   11.695%   $245.6061   $245.61   $245.60   $245.60  
  Purchase #2 $162.94   6.382%   $173.3388   $173.34   $173.35   $173.30  
  Purchase #3 $55.32   4.120%   $57.5992   $57.60   $57.60   $57.60  
  Purchase #4 $22.63   5.520%   $23.8792   $23.88   $23.90   $23.90  
  Purchase #5 $134.85   9.673%   $147.894   $147.89   $147.90   $147.90  
  Purchase #6 $148.55   8.171%   $160.688   $160.69   $160.70   $160.70  
  Purchase #7 $33.68   11.794%   $37.6522   $37.65   $37.65   $37.70  
  7 purchase totals = $777.86       $846.6575   $846.66   $846.70   $846.70