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   13.291%   $56.5889   $56.59   $56.60   $56.60  
  Purchase #2 $44.71   9.379%   $48.9034   $48.90   $48.90   $48.90  
  Purchase #3 $220.35   8.788%   $239.7144   $239.71   $239.70   $239.70  
  Purchase #4 $47.35   5.562%   $49.9836   $49.98   $50.00   $50.00  
  Purchase #5 $175.65   11.273%   $195.451   $195.45   $195.45   $195.50  
  Purchase #6 $200.93   10.222%   $221.4691   $221.47   $221.45   $221.50  
  Purchase #7 $230.81   11.300%   $256.8915   $256.89   $256.90   $256.90  
  7 purchase totals = $969.75       $1,069.0019   $1,068.99   $1,069.00   $1,069.10