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	$93.90	6.432%	$99.9396	$99.94	$99.95	$99.90
Purchase #2	$236.84	3.518%	$245.172	$245.17	$245.15	$245.20
Purchase #3	$172.47	10.141%	$189.9602	$189.96	$189.95	$190.00
Purchase #4	$88.60	12.739%	$99.8868	$99.89	$99.90	$99.90
Purchase #5	$235.91	12.867%	$266.2645	$266.26	$266.25	$266.30
Purchase #6	$10.67	10.292%	$11.7682	$11.77	$11.75	$11.80
Purchase #7	$39.53	4.510%	$41.3128	$41.31	$41.30	$41.30
7 purchase totals =	$877.92		$954.3041	$954.30	$954.25	$954.40