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 $60.49   13.664%   $68.7554   $68.76   $68.75   $68.80  
  Purchase #2 $240.78   9.248%   $263.0473   $263.05   $263.05   $263.00  
  Purchase #3 $167.37   10.155%   $184.3664   $184.37   $184.35   $184.40  
  Purchase #4 $230.31   13.246%   $260.8169   $260.82   $260.80   $260.80  
  Purchase #5 $120.78   6.258%   $128.3384   $128.34   $128.35   $128.30  
  Purchase #6 $44.69   7.156%   $47.888   $47.89   $47.90   $47.90  
  Purchase #7 $27.69   7.318%   $29.7164   $29.72   $29.70   $29.70  
  7 purchase totals = $892.11       $982.9288   $982.95   $982.90   $982.90