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 $156.33   5.174%   $164.4185   $164.42   $164.40   $164.40  
  Purchase #2 $222.41   10.600%   $245.9855   $245.99   $246.00   $246.00  
  Purchase #3 $244.83   5.599%   $258.538   $258.54   $258.55   $258.50  
  Purchase #4 $119.98   3.619%   $124.3221   $124.32   $124.30   $124.30  
  Purchase #5 $15.97   4.356%   $16.6657   $16.67   $16.65   $16.70  
  Purchase #6 $69.60   7.637%   $74.9154   $74.92   $74.90   $74.90  
  Purchase #7 $103.96   4.407%   $108.5415   $108.54   $108.55   $108.50  
  7 purchase totals = $933.08       $993.3867   $993.40   $993.35   $993.30