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	$91.46	12.567%	$102.9538	$102.95	$102.95	$103.00
Purchase #2	$123.62	4.171%	$128.7762	$128.78	$128.80	$128.80
Purchase #3	$233.31	13.535%	$264.8885	$264.89	$264.90	$264.90
Purchase #4	$53.53	5.420%	$56.4313	$56.43	$56.45	$56.40
Purchase #5	$128.56	3.144%	$132.6019	$132.60	$132.60	$132.60
Purchase #6	$156.96	5.444%	$165.5049	$165.50	$165.50	$165.50
Purchase #7	$31.50	5.296%	$33.1682	$33.17	$33.15	$33.20
7 purchase totals =	$818.94		$884.3248	$884.32	$884.35	$884.40