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	$41.32	4.190%	$43.0513	$43.05	$43.05	$43.10
Purchase #2	$77.53	13.436%	$87.9469	$87.95	$87.95	$87.90
Purchase #3	$83.29	8.187%	$90.109	$90.11	$90.10	$90.10
Purchase #4	$111.63	7.361%	$119.8471	$119.85	$119.85	$119.80
Purchase #5	$106.60	12.351%	$119.7662	$119.77	$119.75	$119.80
Purchase #6	$161.32	8.162%	$174.4869	$174.49	$174.50	$174.50
Purchase #7	$152.57	10.710%	$168.9102	$168.91	$168.90	$168.90
7 purchase totals =	$734.26		$804.1176	$804.13	$804.10	$804.10