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 $221.45   7.494%   $238.0455   $238.05   $238.05   $238.00  
  Purchase #2 $117.25   9.387%   $128.2563   $128.26   $128.25   $128.30  
  Purchase #3 $34.41   12.662%   $38.767   $38.77   $38.75   $38.80  
  Purchase #4 $95.41   4.142%   $99.3619   $99.36   $99.35   $99.40  
  Purchase #5 $194.85   7.175%   $208.8305   $208.83   $208.85   $208.80  
  Purchase #6 $53.25   6.844%   $56.8944   $56.89   $56.90   $56.90  
  Purchase #7 $245.55   10.362%   $270.9939   $270.99   $271.00   $271.00  
  7 purchase totals = $962.17       $1,041.1495   $1,041.15   $1,041.15   $1,041.20