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	$82.54	9.425%	$90.3194	$90.32	$90.30	$90.30
Purchase #2	$160.52	9.295%	$175.4403	$175.44	$175.45	$175.40
Purchase #3	$39.76	3.691%	$41.2275	$41.23	$41.25	$41.20
Purchase #4	$221.84	12.278%	$249.0775	$249.08	$249.10	$249.10
Purchase #5	$184.58	5.241%	$194.2538	$194.25	$194.25	$194.30
Purchase #6	$96.28	13.511%	$109.2884	$109.29	$109.30	$109.30
Purchase #7	$35.43	5.863%	$37.5073	$37.51	$37.50	$37.50
7 purchase totals =	$820.95		$897.1142	$897.12	$897.15	$897.10