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	$33.72	6.386%	$35.8734	$35.87	$35.85	$35.90
Purchase #2	$28.89	10.331%	$31.8746	$31.87	$31.85	$31.90
Purchase #3	$112.86	3.539%	$116.8541	$116.85	$116.85	$116.90
Purchase #4	$37.83	3.812%	$39.2721	$39.27	$39.25	$39.30
Purchase #5	$133.84	4.375%	$139.6955	$139.70	$139.70	$139.70
Purchase #6	$80.45	11.441%	$89.6543	$89.65	$89.65	$89.70
Purchase #7	$64.45	7.455%	$69.2547	$69.25	$69.25	$69.30
7 purchase totals =	$492.04		$522.4787	$522.46	$522.40	$522.70