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 $245.54   8.755%   $267.037   $267.04   $267.05   $267.00  
  Purchase #2 $229.61   4.764%   $240.5486   $240.55   $240.55   $240.50  
  Purchase #3 $193.62   7.558%   $208.2538   $208.25   $208.25   $208.30  
  Purchase #4 $85.95   13.776%   $97.7905   $97.79   $97.80   $97.80  
  Purchase #5 $160.32   13.526%   $182.0049   $182.00   $182.00   $182.00  
  Purchase #6 $90.96   4.803%   $95.3288   $95.33   $95.35   $95.30  
  Purchase #7 $230.91   3.462%   $238.9041   $238.90   $238.90   $238.90  
  7 purchase totals = $1,236.91       $1,329.8677   $1,329.86   $1,329.90   $1,329.80