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 $72.61   9.267%   $79.3388   $79.34   $79.35   $79.30  
  Purchase #2 $123.73   10.353%   $136.5398   $136.54   $136.55   $136.50  
  Purchase #3 $61.76   5.547%   $65.1858   $65.19   $65.20   $65.20  
  Purchase #4 $194.74   3.230%   $201.0301   $201.03   $201.05   $201.00  
  Purchase #5 $185.25   8.140%   $200.3294   $200.33   $200.35   $200.30  
  Purchase #6 $95.87   9.525%   $105.0016   $105.00   $105.00   $105.00  
  Purchase #7 $215.32   4.867%   $225.7996   $225.80   $225.80   $225.80  
  7 purchase totals = $949.28       $1,013.2251   $1,013.23   $1,013.30   $1,013.10