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 $244.74   9.523%   $268.0466   $268.05   $268.05   $268.00  
  Purchase #2 $151.61   9.205%   $165.5657   $165.57   $165.55   $165.60  
  Purchase #3 $179.92   7.451%   $193.3258   $193.33   $193.35   $193.30  
  Purchase #4 $211.82   7.162%   $226.9905   $226.99   $227.00   $227.00  
  Purchase #5 $8.74   9.719%   $9.5894   $9.59   $9.60   $9.60  
  Purchase #6 $207.74   9.862%   $228.2273   $228.23   $228.25   $228.20  
  Purchase #7 $245.50   4.149%   $255.6858   $255.69   $255.70   $255.70  
  7 purchase totals = $1,250.07       $1,347.4311   $1,347.45   $1,347.50   $1,347.40