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 $222.69   10.136%   $245.2619   $245.26   $245.25   $245.30  
  Purchase #2 $190.52   13.168%   $215.6077   $215.61   $215.60   $215.60  
  Purchase #3 $183.39   4.702%   $192.013   $192.01   $192.00   $192.00  
  Purchase #4 $158.36   12.761%   $178.5683   $178.57   $178.55   $178.60  
  Purchase #5 $36.38   5.196%   $38.2703   $38.27   $38.25   $38.30  
  Purchase #6 $248.98   11.847%   $278.4767   $278.48   $278.50   $278.50  
  Purchase #7 $55.28   8.624%   $60.0473   $60.05   $60.05   $60.00  
  7 purchase totals = $1,095.60       $1,208.2452   $1,208.25   $1,208.20   $1,208.30