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	$79.80	12.407%	$89.7008	$89.70	$89.70	$89.70
Purchase #2	$22.48	9.267%	$24.5632	$24.56	$24.55	$24.60
Purchase #3	$204.72	9.145%	$223.4416	$223.44	$223.45	$223.40
Purchase #4	$58.83	10.243%	$64.856	$64.86	$64.85	$64.90
Purchase #5	$153.64	8.401%	$166.5473	$166.55	$166.55	$166.50
Purchase #6	$112.77	12.625%	$127.0072	$127.01	$127.00	$127.00
Purchase #7	$180.54	6.323%	$191.9555	$191.96	$191.95	$192.00
7 purchase totals =	$812.78		$888.0716	$888.08	$888.05	$888.10