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	$89.42	12.168%	$100.3006	$100.30	$100.30	$100.30
Purchase #2	$222.60	6.829%	$237.8014	$237.80	$237.80	$237.80
Purchase #3	$88.92	13.608%	$101.0202	$101.02	$101.00	$101.00
Purchase #4	$150.31	11.736%	$167.9504	$167.95	$167.95	$168.00
Purchase #5	$79.36	13.159%	$89.803	$89.80	$89.80	$89.80
Purchase #6	$144.48	3.721%	$149.8561	$149.86	$149.85	$149.90
Purchase #7	$57.64	4.621%	$60.3035	$60.30	$60.30	$60.30
7 purchase totals =	$832.73		$907.0352	$907.03	$907.00	$907.10