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	$108.59	11.106%	$120.65	$120.65	$120.65	$120.70
Purchase #2	$109.76	12.755%	$123.7599	$123.76	$123.75	$123.80
Purchase #3	$238.63	10.327%	$263.2733	$263.27	$263.25	$263.30
Purchase #4	$239.43	11.324%	$266.5431	$266.54	$266.55	$266.50
Purchase #5	$209.75	6.564%	$223.518	$223.52	$223.50	$223.50
Purchase #6	$9.41	11.426%	$10.4852	$10.49	$10.50	$10.50
Purchase #7	$37.65	6.664%	$40.159	$40.16	$40.15	$40.20
7 purchase totals =	$953.22		$1,048.3885	$1,048.39	$1,048.35	$1,048.50