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 $95.43   8.264%   $103.3163   $103.32   $103.30   $103.30  
  Purchase #2 $199.74   3.136%   $206.0038   $206.00   $206.00   $206.00  
  Purchase #3 $56.64   6.497%   $60.3199   $60.32   $60.30   $60.30  
  Purchase #4 $31.95   8.636%   $34.7092   $34.71   $34.70   $34.70  
  Purchase #5 $70.47   3.570%   $72.9858   $72.99   $73.00   $73.00  
  Purchase #6 $192.77   8.213%   $208.6022   $208.60   $208.60   $208.60  
  Purchase #7 $110.49   8.444%   $119.8198   $119.82   $119.80   $119.80  
  7 purchase totals = $757.49       $805.7570   $805.76   $805.70   $805.70