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	$44.26	6.570%	$47.1679	$47.17	$47.15	$47.20
Purchase #2	$60.53	11.229%	$67.3269	$67.33	$67.35	$67.30
Purchase #3	$152.30	12.820%	$171.8249	$171.82	$171.80	$171.80
Purchase #4	$227.73	7.535%	$244.8895	$244.89	$244.90	$244.90
Purchase #5	$217.83	12.741%	$245.5837	$245.58	$245.60	$245.60
Purchase #6	$24.40	10.329%	$26.9203	$26.92	$26.90	$26.90
Purchase #7	$49.37	5.636%	$52.1525	$52.15	$52.15	$52.20
7 purchase totals =	$776.42		$855.8657	$855.86	$855.85	$855.90