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 $193.43   4.463%   $202.0628   $202.06   $202.05   $202.10  
  Purchase #2 $25.82   3.106%   $26.622   $26.62   $26.60   $26.60  
  Purchase #3 $111.79   6.706%   $119.2866   $119.29   $119.30   $119.30  
  Purchase #4 $6.76   6.743%   $7.2158   $7.22   $7.20   $7.20  
  Purchase #5 $212.91   4.629%   $222.7656   $222.77   $222.75   $222.80  
  Purchase #6 $101.82   9.204%   $111.1915   $111.19   $111.20   $111.20  
  Purchase #7 $173.47   11.523%   $193.4589   $193.46   $193.45   $193.50  
  7 purchase totals = $826.00       $882.6032   $882.61   $882.55   $882.70