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 $50.36   6.316%   $53.5407   $53.54   $53.55   $53.50  
  Purchase #2 $26.99   9.868%   $29.6534   $29.65   $29.65   $29.70  
  Purchase #3 $15.60   11.180%   $17.3441   $17.34   $17.35   $17.30  
  Purchase #4 $225.33   3.538%   $233.3022   $233.30   $233.30   $233.30  
  Purchase #5 $202.54   9.573%   $221.9292   $221.93   $221.95   $221.90  
  Purchase #6 $49.29   3.343%   $50.9378   $50.94   $50.95   $50.90  
  Purchase #7 $107.94   4.691%   $113.0035   $113.00   $113.00   $113.00  
  7 purchase totals = $678.05       $719.7109   $719.70   $719.75   $719.60