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 $148.75   3.217%   $153.5353   $153.54   $153.55   $153.50  
  Purchase #2 $50.98   10.693%   $56.4313   $56.43   $56.45   $56.40  
  Purchase #3 $17.36   6.139%   $18.4257   $18.43   $18.45   $18.40  
  Purchase #4 $72.33   9.348%   $79.0914   $79.09   $79.10   $79.10  
  Purchase #5 $153.30   9.234%   $167.4557   $167.46   $167.45   $167.50  
  Purchase #6 $50.28   4.381%   $52.4828   $52.48   $52.50   $52.50  
  Purchase #7 $185.80   12.249%   $208.5586   $208.56   $208.55   $208.60  
  7 purchase totals = $678.80       $735.9808   $735.99   $736.05   $736.00