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 $56.85   5.732%   $60.1086   $60.11   $60.10   $60.10  
  Purchase #2 $190.51   13.754%   $216.7127   $216.71   $216.70   $216.70  
  Purchase #3 $221.28   13.171%   $250.4248   $250.42   $250.40   $250.40  
  Purchase #4 $27.35   4.194%   $28.4971   $28.50   $28.50   $28.50  
  Purchase #5 $184.49   12.784%   $208.0752   $208.08   $208.10   $208.10  
  Purchase #6 $43.63   8.260%   $47.2338   $47.23   $47.25   $47.20  
  Purchase #7 $197.72   7.750%   $213.0433   $213.04   $213.05   $213.00  
  7 purchase totals = $921.83       $1,024.0955   $1,024.09   $1,024.10   $1,024.00