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 $201.89   12.262%   $226.6458   $226.65   $226.65   $226.60  
  Purchase #2 $190.60   10.352%   $210.3309   $210.33   $210.35   $210.30  
  Purchase #3 $108.36   5.803%   $114.6481   $114.65   $114.65   $114.60  
  Purchase #4 $31.57   10.797%   $34.9786   $34.98   $35.00   $35.00  
  Purchase #5 $106.53   10.379%   $117.5867   $117.59   $117.60   $117.60  
  Purchase #6 $232.55   8.466%   $252.2377   $252.24   $252.25   $252.20  
  Purchase #7 $176.59   7.696%   $190.1804   $190.18   $190.20   $190.20  
  7 purchase totals = $1,048.09       $1,146.6082   $1,146.62   $1,146.70   $1,146.50