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	$20.57	4.827%	$21.5629	$21.56	$21.55	$21.60
Purchase #2	$30.88	7.258%	$33.1213	$33.12	$33.10	$33.10
Purchase #3	$196.89	9.309%	$215.2185	$215.22	$215.20	$215.20
Purchase #4	$245.86	9.114%	$268.2677	$268.27	$268.25	$268.30
Purchase #5	$55.47	10.472%	$61.2788	$61.28	$61.30	$61.30
Purchase #6	$187.99	3.285%	$194.1655	$194.17	$194.15	$194.20
Purchase #7	$178.87	3.257%	$184.6958	$184.70	$184.70	$184.70
7 purchase totals =	$916.53		$978.3105	$978.32	$978.25	$978.40