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	$150.35	3.278%	$155.2785	$155.28	$155.30	$155.30
Purchase #2	$43.98	12.859%	$49.6354	$49.64	$49.65	$49.60
Purchase #3	$232.34	4.519%	$242.8394	$242.84	$242.85	$242.80
Purchase #4	$45.85	10.637%	$50.7271	$50.73	$50.75	$50.70
Purchase #5	$89.39	12.731%	$100.7702	$100.77	$100.75	$100.80
Purchase #6	$246.93	13.856%	$281.1446	$281.14	$281.15	$281.10
Purchase #7	$130.46	5.739%	$137.9471	$137.95	$137.95	$137.90
7 purchase totals =	$939.30		$1,018.3423	$1,018.35	$1,018.40	$1,018.20