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	$238.88	12.534%	$268.8212	$268.82	$268.80	$268.80
Purchase #2	$110.38	7.814%	$119.0051	$119.01	$119.00	$119.00
Purchase #3	$173.89	8.592%	$188.8306	$188.83	$188.85	$188.80
Purchase #4	$70.74	12.784%	$79.7834	$79.78	$79.80	$79.80
Purchase #5	$250.38	11.486%	$279.1386	$279.14	$279.15	$279.10
Purchase #6	$82.61	4.372%	$86.2217	$86.22	$86.20	$86.20
Purchase #7	$146.87	3.693%	$152.2939	$152.29	$152.30	$152.30
7 purchase totals =	$1,073.75		$1,174.0945	$1,174.09	$1,174.10	$1,174.00