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 $236.86   13.793%   $269.5301   $269.53   $269.55   $269.50  
  Purchase #2 $44.76   11.609%   $49.9562   $49.96   $49.95   $50.00  
  Purchase #3 $41.47   6.326%   $44.0934   $44.09   $44.10   $44.10  
  Purchase #4 $106.68   7.846%   $115.0501   $115.05   $115.05   $115.10  
  Purchase #5 $114.88   9.266%   $125.5248   $125.52   $125.50   $125.50  
  Purchase #6 $181.55   10.602%   $200.7979   $200.80   $200.80   $200.80  
  Purchase #7 $179.90   4.212%   $187.4774   $187.48   $187.50   $187.50  
  7 purchase totals = $906.10       $992.4299   $992.43   $992.45   $992.50