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 $48.96   12.267%   $54.9659   $54.97   $54.95   $55.00  
  Purchase #2 $45.25   3.111%   $46.6577   $46.66   $46.65   $46.70  
  Purchase #3 $130.94   7.673%   $140.987   $140.99   $141.00   $141.00  
  Purchase #4 $29.41   3.461%   $30.4279   $30.43   $30.45   $30.40  
  Purchase #5 $77.92   5.820%   $82.4549   $82.45   $82.45   $82.50  
  Purchase #6 $201.26   4.653%   $210.6246   $210.62   $210.60   $210.60  
  Purchase #7 $158.76   12.197%   $178.124   $178.12   $178.10   $178.10  
  7 purchase totals = $692.50       $744.2420   $744.24   $744.20   $744.30