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	$81.56	12.522%	$91.7729	$91.77	$91.75	$91.80
Purchase #2	$59.84	13.187%	$67.7311	$67.73	$67.75	$67.70
Purchase #3	$85.60	3.832%	$88.8802	$88.88	$88.90	$88.90
Purchase #4	$48.67	6.651%	$51.907	$51.91	$51.90	$51.90
Purchase #5	$118.41	7.513%	$127.3061	$127.31	$127.30	$127.30
Purchase #6	$19.41	8.580%	$21.0754	$21.08	$21.10	$21.10
Purchase #7	$190.25	3.228%	$196.3913	$196.39	$196.40	$196.40
7 purchase totals =	$603.74		$645.0640	$645.07	$645.10	$645.10