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	$246.72	12.502%	$277.5649	$277.56	$277.55	$277.60
Purchase #2	$172.72	6.715%	$184.3181	$184.32	$184.30	$184.30
Purchase #3	$143.54	12.376%	$161.3045	$161.30	$161.30	$161.30
Purchase #4	$247.64	6.730%	$264.3062	$264.31	$264.30	$264.30
Purchase #5	$18.31	9.587%	$20.0654	$20.07	$20.05	$20.10
Purchase #6	$31.49	12.327%	$35.3718	$35.37	$35.35	$35.40
Purchase #7	$31.40	4.859%	$32.9257	$32.93	$32.95	$32.90
7 purchase totals =	$891.82		$975.8566	$975.86	$975.80	$975.90