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	$57.36	3.844%	$59.5649	$59.56	$59.55	$59.60
Purchase #2	$192.52	8.832%	$209.5234	$209.52	$209.50	$209.50
Purchase #3	$79.37	8.383%	$86.0236	$86.02	$86.00	$86.00
Purchase #4	$200.89	5.185%	$211.3061	$211.31	$211.30	$211.30
Purchase #5	$134.47	12.714%	$151.5665	$151.57	$151.55	$151.60
Purchase #6	$164.46	12.432%	$184.9057	$184.91	$184.90	$184.90
Purchase #7	$53.92	4.476%	$56.3335	$56.33	$56.35	$56.30
7 purchase totals =	$882.99		$959.2237	$959.22	$959.15	$959.20