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 $49.89   12.748%   $56.25   $56.25   $56.25   $56.30  
  Purchase #2 $139.69   8.231%   $151.1879   $151.19   $151.20   $151.20  
  Purchase #3 $218.80   8.102%   $236.5272   $236.53   $236.55   $236.50  
  Purchase #4 $93.28   7.221%   $100.0157   $100.02   $100.00   $100.00  
  Purchase #5 $53.30   13.617%   $60.5579   $60.56   $60.55   $60.60  
  Purchase #6 $103.36   8.567%   $112.2149   $112.21   $112.20   $112.20  
  Purchase #7 $48.37   9.598%   $53.0126   $53.01   $53.00   $53.00  
  7 purchase totals = $706.69       $769.7662   $769.77   $769.75   $769.80