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 $110.99   13.539%   $126.0169   $126.02   $126.00   $126.00  
  Purchase #2 $117.40   4.131%   $122.2498   $122.25   $122.25   $122.20  
  Purchase #3 $77.39   12.383%   $86.9732   $86.97   $86.95   $87.00  
  Purchase #4 $106.72   9.275%   $116.6183   $116.62   $116.60   $116.60  
  Purchase #5 $84.85   11.264%   $94.4075   $94.41   $94.40   $94.40  
  Purchase #6 $11.85   8.274%   $12.8305   $12.83   $12.85   $12.80  
  Purchase #7 $201.54   6.449%   $214.5373   $214.54   $214.55   $214.50  
  7 purchase totals = $710.74       $773.6335   $773.64   $773.60   $773.50