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	$83.79	5.639%	$88.5149	$88.51	$88.50	$88.50
Purchase #2	$100.47	3.328%	$103.8136	$103.81	$103.80	$103.80
Purchase #3	$179.78	6.696%	$191.8181	$191.82	$191.80	$191.80
Purchase #4	$59.64	9.251%	$65.1573	$65.16	$65.15	$65.20
Purchase #5	$30.27	13.558%	$34.374	$34.37	$34.35	$34.40
Purchase #6	$34.26	12.539%	$38.5559	$38.56	$38.55	$38.60
Purchase #7	$52.41	12.481%	$58.9513	$58.95	$58.95	$59.00
7 purchase totals =	$540.62		$581.1851	$581.18	$581.10	$581.30