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	$156.93	7.614%	$168.8787	$168.88	$168.90	$168.90
Purchase #2	$57.87	3.508%	$59.9001	$59.90	$59.90	$59.90
Purchase #3	$91.64	8.773%	$99.6796	$99.68	$99.70	$99.70
Purchase #4	$101.28	9.322%	$110.7213	$110.72	$110.70	$110.70
Purchase #5	$140.65	12.806%	$158.6616	$158.66	$158.65	$158.70
Purchase #6	$6.77	4.870%	$7.0997	$7.10	$7.10	$7.10
Purchase #7	$5.94	7.281%	$6.3725	$6.37	$6.35	$6.40
7 purchase totals =	$561.08		$611.3135	$611.31	$611.30	$611.40