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 $117.78   5.451%   $124.2002   $124.20   $124.20   $124.20  
  Purchase #2 $60.29   9.743%   $66.1641   $66.16   $66.15   $66.20  
  Purchase #3 $167.78   6.345%   $178.4256   $178.43   $178.45   $178.40  
  Purchase #4 $173.30   13.830%   $197.2674   $197.27   $197.25   $197.30  
  Purchase #5 $89.47   4.824%   $93.786   $93.79   $93.80   $93.80  
  Purchase #6 $184.97   3.439%   $191.3311   $191.33   $191.35   $191.30  
  Purchase #7 $198.58   12.166%   $222.7392   $222.74   $222.75   $222.70  
  7 purchase totals = $992.17       $1,073.9136   $1,073.92   $1,073.95   $1,073.90