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 $61.94   13.496%   $70.2994   $70.30   $70.30   $70.30  
  Purchase #2 $14.75   11.252%   $16.4097   $16.41   $16.40   $16.40  
  Purchase #3 $150.98   9.178%   $164.8369   $164.84   $164.85   $164.80  
  Purchase #4 $64.37   12.586%   $72.4716   $72.47   $72.45   $72.50  
  Purchase #5 $124.37   10.722%   $137.705   $137.71   $137.70   $137.70  
  Purchase #6 $196.76   5.732%   $208.0383   $208.04   $208.05   $208.00  
  Purchase #7 $200.42   10.751%   $221.9672   $221.97   $221.95   $222.00  
  7 purchase totals = $813.59       $891.7281   $891.74   $891.70   $891.70