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	$78.42	8.569%	$85.1398	$85.14	$85.15	$85.10
Purchase #2	$26.42	5.507%	$27.8749	$27.87	$27.85	$27.90
Purchase #3	$130.80	8.183%	$141.5034	$141.50	$141.50	$141.50
Purchase #4	$134.34	5.586%	$141.8442	$141.84	$141.85	$141.80
Purchase #5	$75.83	12.488%	$85.2997	$85.30	$85.30	$85.30
Purchase #6	$86.51	6.850%	$92.4359	$92.44	$92.45	$92.40
Purchase #7	$18.80	8.735%	$20.4422	$20.44	$20.45	$20.40
7 purchase totals =	$551.12		$594.5401	$594.53	$594.55	$594.40