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	$142.80	5.790%	$151.0681	$151.07	$151.05	$151.10
Purchase #2	$32.53	8.267%	$35.2193	$35.22	$35.20	$35.20
Purchase #3	$232.80	4.159%	$242.4822	$242.48	$242.50	$242.50
Purchase #4	$115.75	6.597%	$123.386	$123.39	$123.40	$123.40
Purchase #5	$111.37	10.565%	$123.1362	$123.14	$123.15	$123.10
Purchase #6	$46.39	5.396%	$48.8932	$48.89	$48.90	$48.90
Purchase #7	$242.62	11.382%	$270.235	$270.24	$270.25	$270.20
7 purchase totals =	$924.26		$994.4200	$994.43	$994.45	$994.40