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 $76.93   12.531%   $86.5701   $86.57   $86.55   $86.60  
  Purchase #2 $46.38   8.858%   $50.4883   $50.49   $50.50   $50.50  
  Purchase #3 $72.36   12.855%   $81.6619   $81.66   $81.65   $81.70  
  Purchase #4 $241.58   12.463%   $271.6881   $271.69   $271.70   $271.70  
  Purchase #5 $200.99   9.297%   $219.676   $219.68   $219.70   $219.70  
  Purchase #6 $162.73   8.350%   $176.318   $176.32   $176.30   $176.30  
  Purchase #7 $165.56   7.281%   $177.6144   $177.61   $177.60   $177.60  
  7 purchase totals = $966.53       $1,064.0168   $1,064.02   $1,064.00   $1,064.10