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	$106.31	10.419%	$117.3864	$117.39	$117.40	$117.40
Purchase #2	$63.49	10.454%	$70.1272	$70.13	$70.15	$70.10
Purchase #3	$52.77	12.650%	$59.4454	$59.45	$59.45	$59.40
Purchase #4	$6.47	10.680%	$7.161	$7.16	$7.15	$7.20
Purchase #5	$210.47	6.390%	$223.919	$223.92	$223.90	$223.90
Purchase #6	$228.63	7.542%	$245.8733	$245.87	$245.85	$245.90
Purchase #7	$109.55	12.294%	$123.0181	$123.02	$123.00	$123.00
7 purchase totals =	$777.69		$846.9304	$846.94	$846.90	$846.90