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	$29.87	9.654%	$32.7536	$32.75	$32.75	$32.80
Purchase #2	$194.68	9.217%	$212.6237	$212.62	$212.60	$212.60
Purchase #3	$48.77	11.376%	$54.3181	$54.32	$54.30	$54.30
Purchase #4	$80.86	10.468%	$89.3244	$89.32	$89.30	$89.30
Purchase #5	$212.87	10.229%	$234.6445	$234.64	$234.65	$234.60
Purchase #6	$197.46	3.621%	$204.61	$204.61	$204.60	$204.60
Purchase #7	$32.98	7.567%	$35.4756	$35.48	$35.50	$35.50
7 purchase totals =	$797.49		$863.7499	$863.74	$863.70	$863.70