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	$244.76	8.211%	$264.8572	$264.86	$264.85	$264.90
Purchase #2	$38.36	12.687%	$43.2267	$43.23	$43.25	$43.20
Purchase #3	$12.79	6.515%	$13.6233	$13.62	$13.60	$13.60
Purchase #4	$136.89	12.110%	$153.4674	$153.47	$153.45	$153.50
Purchase #5	$165.42	9.344%	$180.8768	$180.88	$180.90	$180.90
Purchase #6	$149.93	3.534%	$155.2285	$155.23	$155.25	$155.20
Purchase #7	$19.74	6.501%	$21.0233	$21.02	$21.00	$21.00
7 purchase totals =	$767.89		$832.3032	$832.31	$832.30	$832.30