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 $93.55   8.773%   $101.7571   $101.76   $101.75   $101.80  
  Purchase #2 $182.34   6.198%   $193.6414   $193.64   $193.65   $193.60  
  Purchase #3 $213.48   12.695%   $240.5813   $240.58   $240.60   $240.60  
  Purchase #4 $143.60   10.456%   $158.6148   $158.61   $158.60   $158.60  
  Purchase #5 $8.84   11.492%   $9.8559   $9.86   $9.85   $9.90  
  Purchase #6 $57.41   13.343%   $65.0702   $65.07   $65.05   $65.10  
  Purchase #7 $205.93   7.760%   $221.9102   $221.91   $221.90   $221.90  
  7 purchase totals = $905.15       $991.4309   $991.43   $991.40   $991.50