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 $188.43   9.474%   $206.2819   $206.28   $206.30   $206.30  
  Purchase #2 $177.68   5.244%   $186.9975   $187.00   $187.00   $187.00  
  Purchase #3 $11.37   10.756%   $12.593   $12.59   $12.60   $12.60  
  Purchase #4 $40.43   12.302%   $45.4037   $45.40   $45.40   $45.40  
  Purchase #5 $228.70   5.818%   $242.0058   $242.01   $242.00   $242.00  
  Purchase #6 $66.98   4.509%   $70.0001   $70.00   $70.00   $70.00  
  Purchase #7 $184.74   3.483%   $191.1745   $191.17   $191.15   $191.20  
  7 purchase totals = $898.33       $954.4565   $954.45   $954.45   $954.50