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 $95.50   11.629%   $106.6057   $106.61   $106.60   $106.60  
  Purchase #2 $146.48   13.315%   $165.9838   $165.98   $166.00   $166.00  
  Purchase #3 $86.49   6.862%   $92.4249   $92.42   $92.40   $92.40  
  Purchase #4 $50.97   3.394%   $52.6999   $52.70   $52.70   $52.70  
  Purchase #5 $104.72   10.106%   $115.303   $115.30   $115.30   $115.30  
  Purchase #6 $245.73   9.730%   $269.6395   $269.64   $269.65   $269.60  
  Purchase #7 $196.47   4.356%   $205.0282   $205.03   $205.05   $205.00  
  7 purchase totals = $926.36       $1,007.6850   $1,007.68   $1,007.70   $1,007.60