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	$156.58	5.561%	$165.2874	$165.29	$165.30	$165.30
Purchase #2	$165.29	7.270%	$177.3066	$177.31	$177.30	$177.30
Purchase #3	$39.83	7.421%	$42.7858	$42.79	$42.80	$42.80
Purchase #4	$73.83	12.110%	$82.7708	$82.77	$82.75	$82.80
Purchase #5	$220.50	9.472%	$241.3858	$241.39	$241.40	$241.40
Purchase #6	$174.99	9.432%	$191.4951	$191.50	$191.50	$191.50
Purchase #7	$229.25	11.256%	$255.0544	$255.05	$255.05	$255.10
7 purchase totals =	$1,060.27		$1,156.0859	$1,156.10	$1,156.10	$1,156.20