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	$92.95	10.346%	$102.5666	$102.57	$102.55	$102.60
Purchase #2	$28.68	8.829%	$31.2122	$31.21	$31.20	$31.20
Purchase #3	$194.86	8.625%	$211.6667	$211.67	$211.65	$211.70
Purchase #4	$75.83	12.396%	$85.2299	$85.23	$85.25	$85.20
Purchase #5	$166.97	7.275%	$179.1171	$179.12	$179.10	$179.10
Purchase #6	$118.86	4.183%	$123.8319	$123.83	$123.85	$123.80
Purchase #7	$96.88	5.170%	$101.8887	$101.89	$101.90	$101.90
7 purchase totals =	$775.03		$835.5131	$835.52	$835.50	$835.50