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 $213.71   10.442%   $236.0256   $236.03   $236.05   $236.00  
  Purchase #2 $89.48   5.275%   $94.2001   $94.20   $94.20   $94.20  
  Purchase #3 $33.74   7.649%   $36.3208   $36.32   $36.30   $36.30  
  Purchase #4 $125.95   6.810%   $134.5272   $134.53   $134.55   $134.50  
  Purchase #5 $138.93   12.514%   $156.3157   $156.32   $156.30   $156.30  
  Purchase #6 $125.32   7.812%   $135.11   $135.11   $135.10   $135.10  
  Purchase #7 $156.90   10.768%   $173.795   $173.80   $173.80   $173.80  
  7 purchase totals = $884.03       $966.2944   $966.31   $966.30   $966.20