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 $108.95   8.631%   $118.3535   $118.35   $118.35   $118.40  
  Purchase #2 $223.68   12.240%   $251.0584   $251.06   $251.05   $251.10  
  Purchase #3 $199.80   3.140%   $206.0737   $206.07   $206.05   $206.10  
  Purchase #4 $66.33   12.677%   $74.7387   $74.74   $74.75   $74.70  
  Purchase #5 $101.61   8.157%   $109.8983   $109.90   $109.90   $109.90  
  Purchase #6 $186.61   3.517%   $193.1731   $193.17   $193.15   $193.20  
  Purchase #7 $186.86   10.470%   $206.4242   $206.42   $206.40   $206.40  
  7 purchase totals = $1,073.84       $1,159.7199   $1,159.71   $1,159.65   $1,159.80