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 $232.48   6.561%   $247.733   $247.73   $247.75   $247.70  
  Purchase #2 $61.85   8.189%   $66.9149   $66.91   $66.90   $66.90  
  Purchase #3 $177.78   3.867%   $184.6548   $184.65   $184.65   $184.70  
  Purchase #4 $169.41   10.694%   $187.5267   $187.53   $187.55   $187.50  
  Purchase #5 $213.56   12.376%   $239.9902   $239.99   $240.00   $240.00  
  Purchase #6 $250.53   10.430%   $276.6603   $276.66   $276.65   $276.70  
  Purchase #7 $6.43   9.780%   $7.0589   $7.06   $7.05   $7.10  
  7 purchase totals = $1,112.04       $1,210.5388   $1,210.53   $1,210.55   $1,210.60