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 $58.35   6.279%   $62.0138   $62.01   $62.00   $62.00  
  Purchase #2 $40.94   8.139%   $44.2721   $44.27   $44.25   $44.30  
  Purchase #3 $230.26   4.108%   $239.7191   $239.72   $239.70   $239.70  
  Purchase #4 $176.64   9.144%   $192.792   $192.79   $192.80   $192.80  
  Purchase #5 $23.95   13.430%   $27.1665   $27.17   $27.15   $27.20  
  Purchase #6 $123.94   6.361%   $131.8238   $131.82   $131.80   $131.80  
  Purchase #7 $151.83   7.323%   $162.9485   $162.95   $162.95   $162.90  
  7 purchase totals = $805.91       $860.7358   $860.73   $860.65   $860.70