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 $232.90   3.351%   $240.7045   $240.70   $240.70   $240.70  
  Purchase #2 $10.89   3.321%   $11.2517   $11.25   $11.25   $11.30  
  Purchase #3 $191.50   5.769%   $202.5476   $202.55   $202.55   $202.50  
  Purchase #4 $50.27   5.222%   $52.8951   $52.90   $52.90   $52.90  
  Purchase #5 $214.49   10.538%   $237.093   $237.09   $237.10   $237.10  
  Purchase #6 $100.76   5.267%   $106.067   $106.07   $106.05   $106.10  
  Purchase #7 $219.35   12.325%   $246.3849   $246.38   $246.40   $246.40  
  7 purchase totals = $1,020.16       $1,096.9438   $1,096.94   $1,096.95   $1,097.00