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 $17.65   11.209%   $19.6284   $19.63   $19.65   $19.60  
  Purchase #2 $208.58   11.280%   $232.1078   $232.11   $232.10   $232.10  
  Purchase #3 $58.36   7.450%   $62.7078   $62.71   $62.70   $62.70  
  Purchase #4 $232.89   7.304%   $249.9003   $249.90   $249.90   $249.90  
  Purchase #5 $241.55   10.577%   $267.0987   $267.10   $267.10   $267.10  
  Purchase #6 $51.67   6.349%   $54.9505   $54.95   $54.95   $55.00  
  Purchase #7 $150.49   8.373%   $163.0905   $163.09   $163.10   $163.10  
  7 purchase totals = $961.19       $1,049.4840   $1,049.49   $1,049.50   $1,049.50