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 $83.44   4.166%   $86.9161   $86.92   $86.90   $86.90  
  Purchase #2 $179.55   3.256%   $185.3961   $185.40   $185.40   $185.40  
  Purchase #3 $120.99   3.555%   $125.2912   $125.29   $125.30   $125.30  
  Purchase #4 $209.95   3.361%   $217.0064   $217.01   $217.00   $217.00  
  Purchase #5 $206.86   3.278%   $213.6409   $213.64   $213.65   $213.60  
  Purchase #6 $41.63   4.244%   $43.3968   $43.40   $43.40   $43.40  
  Purchase #7 $23.99   5.270%   $25.2543   $25.25   $25.25   $25.30  
  7 purchase totals = $866.41       $896.9018   $896.91   $896.90   $896.90