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 $194.49   7.459%   $208.997   $209.00   $209.00   $209.00  
  Purchase #2 $7.73   9.524%   $8.4662   $8.47   $8.45   $8.50  
  Purchase #3 $15.37   7.398%   $16.5071   $16.51   $16.50   $16.50  
  Purchase #4 $48.35   4.403%   $50.4789   $50.48   $50.50   $50.50  
  Purchase #5 $50.63   6.310%   $53.8248   $53.82   $53.80   $53.80  
  Purchase #6 $10.84   11.561%   $12.0932   $12.09   $12.10   $12.10  
  Purchase #7 $32.39   12.151%   $36.3257   $36.33   $36.35   $36.30  
  7 purchase totals = $359.80       $386.6929   $386.70   $386.70   $386.70