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 $69.68   6.156%   $73.9695   $73.97   $73.95   $74.00  
  Purchase #2 $144.85   7.598%   $155.8557   $155.86   $155.85   $155.90  
  Purchase #3 $141.39   3.203%   $145.9187   $145.92   $145.90   $145.90  
  Purchase #4 $53.76   6.586%   $57.3006   $57.30   $57.30   $57.30  
  Purchase #5 $53.47   6.349%   $56.8648   $56.86   $56.85   $56.90  
  Purchase #6 $85.91   7.346%   $92.2209   $92.22   $92.20   $92.20  
  Purchase #7 $72.68   7.131%   $77.8628   $77.86   $77.85   $77.90  
  7 purchase totals = $621.74       $659.9930   $659.99   $659.90   $660.10