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 $60.41   3.586%   $62.5763   $62.58   $62.60   $62.60  
  Purchase #2 $163.46   5.452%   $172.3718   $172.37   $172.35   $172.40  
  Purchase #3 $152.78   8.155%   $165.2392   $165.24   $165.25   $165.20  
  Purchase #4 $103.72   11.465%   $115.6115   $115.61   $115.60   $115.60  
  Purchase #5 $233.29   12.734%   $262.9971   $263.00   $263.00   $263.00  
  Purchase #6 $50.79   13.390%   $57.5908   $57.59   $57.60   $57.60  
  Purchase #7 $150.40   8.561%   $163.2757   $163.28   $163.30   $163.30  
  7 purchase totals = $914.85       $999.6624   $999.67   $999.70   $999.70