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 $184.41   11.715%   $206.0136   $206.01   $206.00   $206.00  
  Purchase #2 $185.27   6.650%   $197.5905   $197.59   $197.60   $197.60  
  Purchase #3 $77.44   7.792%   $83.4741   $83.47   $83.45   $83.50  
  Purchase #4 $8.52   10.179%   $9.3873   $9.39   $9.40   $9.40  
  Purchase #5 $30.75   11.541%   $34.2989   $34.30   $34.30   $34.30  
  Purchase #6 $14.52   5.382%   $15.3015   $15.30   $15.30   $15.30  
  Purchase #7 $64.89   4.839%   $68.03   $68.03   $68.05   $68.00  
  7 purchase totals = $565.80       $614.0959   $614.09   $614.10   $614.10