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 $62.31   6.231%   $66.1925   $66.19   $66.20   $66.20  
  Purchase #2 $125.83   7.613%   $135.4094   $135.41   $135.40   $135.40  
  Purchase #3 $56.83   7.755%   $61.2372   $61.24   $61.25   $61.20  
  Purchase #4 $36.28   12.752%   $40.9064   $40.91   $40.90   $40.90  
  Purchase #5 $239.75   9.802%   $263.2503   $263.25   $263.25   $263.30  
  Purchase #6 $206.96   4.776%   $216.8444   $216.84   $216.85   $216.80  
  Purchase #7 $231.64   3.672%   $240.1458   $240.15   $240.15   $240.10  
  7 purchase totals = $959.60       $1,023.9860   $1,023.99   $1,024.00   $1,023.90