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	$110.34	11.577%	$123.1141	$123.11	$123.10	$123.10
Purchase #2	$142.31	12.846%	$160.5911	$160.59	$160.60	$160.60
Purchase #3	$151.89	12.258%	$170.5087	$170.51	$170.50	$170.50
Purchase #4	$100.83	8.560%	$109.461	$109.46	$109.45	$109.50
Purchase #5	$77.54	8.128%	$83.8425	$83.84	$83.85	$83.80
Purchase #6	$228.40	6.849%	$244.0431	$244.04	$244.05	$244.00
Purchase #7	$243.72	4.656%	$255.0676	$255.07	$255.05	$255.10
7 purchase totals =	$1,055.03		$1,146.6281	$1,146.62	$1,146.60	$1,146.60