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	$231.33	6.618%	$246.6394	$246.64	$246.65	$246.60
Purchase #2	$92.65	11.397%	$103.2093	$103.21	$103.20	$103.20
Purchase #3	$157.29	13.174%	$178.0114	$178.01	$178.00	$178.00
Purchase #4	$6.93	4.399%	$7.2349	$7.23	$7.25	$7.20
Purchase #5	$31.62	12.442%	$35.5542	$35.55	$35.55	$35.60
Purchase #6	$18.42	10.172%	$20.2937	$20.29	$20.30	$20.30
Purchase #7	$229.39	11.212%	$255.1092	$255.11	$255.10	$255.10
7 purchase totals =	$767.63		$846.0521	$846.04	$846.05	$846.00