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	$52.80	10.686%	$58.4422	$58.44	$58.45	$58.40
Purchase #2	$181.84	4.660%	$190.3137	$190.31	$190.30	$190.30
Purchase #3	$39.46	7.196%	$42.2995	$42.30	$42.30	$42.30
Purchase #4	$89.51	11.236%	$99.5673	$99.57	$99.55	$99.60
Purchase #5	$132.96	8.802%	$144.6631	$144.66	$144.65	$144.70
Purchase #6	$96.36	3.386%	$99.6227	$99.62	$99.60	$99.60
Purchase #7	$118.91	10.485%	$131.3777	$131.38	$131.40	$131.40
7 purchase totals =	$711.84		$766.2862	$766.28	$766.25	$766.30