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 $59.98   6.398%   $63.8175   $63.82   $63.80   $63.80  
  Purchase #2 $184.34   4.409%   $192.4676   $192.47   $192.45   $192.50  
  Purchase #3 $12.45   6.119%   $13.2118   $13.21   $13.20   $13.20  
  Purchase #4 $35.54   7.160%   $38.0847   $38.08   $38.10   $38.10  
  Purchase #5 $55.54   8.449%   $60.2326   $60.23   $60.25   $60.20  
  Purchase #6 $240.90   5.309%   $253.6894   $253.69   $253.70   $253.70  
  Purchase #7 $102.58   7.159%   $109.9237   $109.92   $109.90   $109.90  
  7 purchase totals = $691.33       $731.4273   $731.42   $731.40   $731.40