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 $62.55   10.167%   $68.9095   $68.91   $68.90   $68.90  
  Purchase #2 $75.55   12.874%   $85.2763   $85.28   $85.30   $85.30  
  Purchase #3 $6.76   4.128%   $7.0391   $7.04   $7.05   $7.00  
  Purchase #4 $46.93   13.765%   $53.3899   $53.39   $53.40   $53.40  
  Purchase #5 $238.66   6.326%   $253.7576   $253.76   $253.75   $253.80  
  Purchase #6 $76.58   5.450%   $80.7536   $80.75   $80.75   $80.80  
  Purchase #7 $167.61   4.233%   $174.7049   $174.70   $174.70   $174.70  
  7 purchase totals = $674.64       $723.8309   $723.83   $723.85   $723.90