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 $143.33   3.127%   $147.8119   $147.81   $147.80   $147.80  
  Purchase #2 $115.47   3.129%   $119.0831   $119.08   $119.10   $119.10  
  Purchase #3 $192.84   11.867%   $215.7243   $215.72   $215.70   $215.70  
  Purchase #4 $13.26   13.480%   $15.0474   $15.05   $15.05   $15.00  
  Purchase #5 $134.69   5.570%   $142.1922   $142.19   $142.20   $142.20  
  Purchase #6 $79.74   7.780%   $85.9438   $85.94   $85.95   $85.90  
  Purchase #7 $54.87   10.321%   $60.5331   $60.53   $60.55   $60.50  
  7 purchase totals = $734.20       $786.3358   $786.32   $786.35   $786.20