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	$91.99	8.145%	$99.4826	$99.48	$99.50	$99.50
Purchase #2	$53.28	8.689%	$57.9095	$57.91	$57.90	$57.90
Purchase #3	$37.96	4.342%	$39.6082	$39.61	$39.60	$39.60
Purchase #4	$197.82	12.679%	$222.9016	$222.90	$222.90	$222.90
Purchase #5	$51.70	10.842%	$57.3053	$57.31	$57.30	$57.30
Purchase #6	$9.51	10.862%	$10.543	$10.54	$10.55	$10.50
Purchase #7	$119.27	3.721%	$123.708	$123.71	$123.70	$123.70
7 purchase totals =	$561.53		$611.4582	$611.46	$611.45	$611.40