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	$39.46	8.749%	$42.9124	$42.91	$42.90	$42.90
Purchase #2	$42.64	10.485%	$47.1108	$47.11	$47.10	$47.10
Purchase #3	$210.30	8.211%	$227.5677	$227.57	$227.55	$227.60
Purchase #4	$229.86	5.583%	$242.6931	$242.69	$242.70	$242.70
Purchase #5	$128.94	6.653%	$137.5184	$137.52	$137.50	$137.50
Purchase #6	$42.90	13.337%	$48.6216	$48.62	$48.60	$48.60
Purchase #7	$31.56	13.148%	$35.7095	$35.71	$35.70	$35.70
7 purchase totals =	$725.66		$782.1335	$782.13	$782.05	$782.10