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	$198.46	12.229%	$222.7297	$222.73	$222.75	$222.70
Purchase #2	$51.61	6.188%	$54.8036	$54.80	$54.80	$54.80
Purchase #3	$111.84	10.550%	$123.6391	$123.64	$123.65	$123.60
Purchase #4	$99.66	12.744%	$112.3607	$112.36	$112.35	$112.40
Purchase #5	$6.68	7.608%	$7.1882	$7.19	$7.20	$7.20
Purchase #6	$9.35	13.549%	$10.6168	$10.62	$10.60	$10.60
Purchase #7	$229.80	10.310%	$253.4924	$253.49	$253.50	$253.50
7 purchase totals =	$707.40		$784.8305	$784.83	$784.85	$784.80