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	$80.91	10.600%	$89.4865	$89.49	$89.50	$89.50
Purchase #2	$246.38	5.841%	$260.7711	$260.77	$260.75	$260.80
Purchase #3	$32.46	7.701%	$34.9597	$34.96	$34.95	$35.00
Purchase #4	$16.58	12.445%	$18.6434	$18.64	$18.65	$18.60
Purchase #5	$141.82	6.705%	$151.329	$151.33	$151.35	$151.30
Purchase #6	$18.75	7.268%	$20.1128	$20.11	$20.10	$20.10
Purchase #7	$97.59	8.740%	$106.1194	$106.12	$106.10	$106.10
7 purchase totals =	$634.49		$681.4219	$681.42	$681.40	$681.40