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	$166.29	4.141%	$173.1761	$173.18	$173.20	$173.20
Purchase #2	$88.27	12.407%	$99.2217	$99.22	$99.20	$99.20
Purchase #3	$222.54	3.291%	$229.8638	$229.86	$229.85	$229.90
Purchase #4	$119.86	11.513%	$133.6595	$133.66	$133.65	$133.70
Purchase #5	$89.37	3.269%	$92.2915	$92.29	$92.30	$92.30
Purchase #6	$52.80	11.843%	$59.0531	$59.05	$59.05	$59.10
Purchase #7	$47.35	6.711%	$50.5277	$50.53	$50.55	$50.50
7 purchase totals =	$786.48		$837.7934	$837.79	$837.80	$837.90