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 $101.47   5.716%   $107.27   $107.27   $107.25   $107.30  
  Purchase #2 $77.55   5.722%   $81.9874   $81.99   $82.00   $82.00  
  Purchase #3 $14.27   6.551%   $15.2048   $15.20   $15.20   $15.20  
  Purchase #4 $87.34   7.450%   $93.8468   $93.85   $93.85   $93.80  
  Purchase #5 $170.63   8.827%   $185.6915   $185.69   $185.70   $185.70  
  Purchase #6 $193.34   8.275%   $209.3389   $209.34   $209.35   $209.30  
  Purchase #7 $147.38   7.835%   $158.9272   $158.93   $158.95   $158.90  
  7 purchase totals = $791.98       $852.2666   $852.27   $852.30   $852.20