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	$77.74	9.286%	$84.9589	$84.96	$84.95	$85.00
Purchase #2	$116.75	11.268%	$129.9054	$129.91	$129.90	$129.90
Purchase #3	$103.40	5.326%	$108.9071	$108.91	$108.90	$108.90
Purchase #4	$114.96	11.823%	$128.5517	$128.55	$128.55	$128.60
Purchase #5	$56.67	4.558%	$59.253	$59.25	$59.25	$59.30
Purchase #6	$77.25	8.271%	$83.6393	$83.64	$83.65	$83.60
Purchase #7	$177.36	10.740%	$196.4085	$196.41	$196.40	$196.40
7 purchase totals =	$724.13		$791.6239	$791.63	$791.60	$791.70