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	$45.93	10.551%	$50.7761	$50.78	$50.80	$50.80
Purchase #2	$38.73	13.473%	$43.9481	$43.95	$43.95	$43.90
Purchase #3	$207.26	10.707%	$229.4513	$229.45	$229.45	$229.50
Purchase #4	$92.31	7.105%	$98.8686	$98.87	$98.85	$98.90
Purchase #5	$40.82	5.413%	$43.0296	$43.03	$43.05	$43.00
Purchase #6	$61.45	3.562%	$63.6388	$63.64	$63.65	$63.60
Purchase #7	$223.89	8.682%	$243.3281	$243.33	$243.35	$243.30
7 purchase totals =	$710.39		$773.0406	$773.05	$773.10	$773.00