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	$142.55	4.219%	$148.5642	$148.56	$148.55	$148.60
Purchase #2	$173.49	12.828%	$195.7453	$195.75	$195.75	$195.70
Purchase #3	$176.91	13.562%	$200.9025	$200.90	$200.90	$200.90
Purchase #4	$132.35	8.698%	$143.8618	$143.86	$143.85	$143.90
Purchase #5	$91.53	13.279%	$103.6843	$103.68	$103.70	$103.70
Purchase #6	$31.55	12.720%	$35.5632	$35.56	$35.55	$35.60
Purchase #7	$81.62	9.298%	$89.209	$89.21	$89.20	$89.20
7 purchase totals =	$830.00		$917.5303	$917.52	$917.50	$917.60