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 $56.85   5.812%   $60.1541   $60.15   $60.15   $60.20  
  Purchase #2 $99.88   9.436%   $109.3047   $109.30   $109.30   $109.30  
  Purchase #3 $59.28   8.618%   $64.3888   $64.39   $64.40   $64.40  
  Purchase #4 $44.94   6.697%   $47.9496   $47.95   $47.95   $47.90  
  Purchase #5 $242.59   12.565%   $273.0714   $273.07   $273.05   $273.10  
  Purchase #6 $233.62   6.491%   $248.7843   $248.78   $248.80   $248.80  
  Purchase #7 $239.56   5.759%   $253.3563   $253.36   $253.35   $253.40  
  7 purchase totals = $976.72       $1,057.0092   $1,057.00   $1,057.00   $1,057.10