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 $141.39   8.193%   $152.9741   $152.97   $152.95   $153.00  
  Purchase #2 $197.55   13.623%   $224.4622   $224.46   $224.45   $224.50  
  Purchase #3 $51.36   12.690%   $57.8776   $57.88   $57.90   $57.90  
  Purchase #4 $60.90   8.821%   $66.272   $66.27   $66.25   $66.30  
  Purchase #5 $250.57   7.211%   $268.6386   $268.64   $268.65   $268.60  
  Purchase #6 $178.51   9.696%   $195.8183   $195.82   $195.80   $195.80  
  Purchase #7 $28.63   8.522%   $31.0698   $31.07   $31.05   $31.10  
  7 purchase totals = $908.91       $997.1126   $997.11   $997.05   $997.20