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	$172.98	6.208%	$183.7186	$183.72	$183.70	$183.70
Purchase #2	$95.88	9.305%	$104.8016	$104.80	$104.80	$104.80
Purchase #3	$17.43	13.199%	$19.7306	$19.73	$19.75	$19.70
Purchase #4	$7.43	11.292%	$8.269	$8.27	$8.25	$8.30
Purchase #5	$190.35	3.212%	$196.464	$196.46	$196.45	$196.50
Purchase #6	$210.42	9.731%	$230.896	$230.90	$230.90	$230.90
Purchase #7	$76.37	7.835%	$82.3536	$82.35	$82.35	$82.40
7 purchase totals =	$770.86		$826.2334	$826.23	$826.20	$826.30