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 $49.95   12.664%   $56.2757   $56.28   $56.30   $56.30  
  Purchase #2 $196.69   13.395%   $223.0366   $223.04   $223.05   $223.00  
  Purchase #3 $53.29   10.793%   $59.0416   $59.04   $59.05   $59.00  
  Purchase #4 $180.67   3.399%   $186.811   $186.81   $186.80   $186.80  
  Purchase #5 $161.72   11.334%   $180.0493   $180.05   $180.05   $180.00  
  Purchase #6 $188.29   7.722%   $202.8298   $202.83   $202.85   $202.80  
  Purchase #7 $64.84   13.788%   $73.7801   $73.78   $73.80   $73.80  
  7 purchase totals = $895.45       $981.8241   $981.83   $981.90   $981.70