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	$166.76	12.578%	$187.7351	$187.74	$187.75	$187.70
Purchase #2	$33.80	11.243%	$37.6001	$37.60	$37.60	$37.60
Purchase #3	$139.71	13.172%	$158.1126	$158.11	$158.10	$158.10
Purchase #4	$150.26	12.658%	$169.2799	$169.28	$169.30	$169.30
Purchase #5	$42.75	3.546%	$44.2659	$44.27	$44.25	$44.30
Purchase #6	$150.36	3.189%	$155.155	$155.16	$155.15	$155.20
Purchase #7	$141.54	10.827%	$156.8645	$156.86	$156.85	$156.90
7 purchase totals =	$825.18		$909.0131	$909.02	$909.00	$909.10