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	$53.27	13.310%	$60.3602	$60.36	$60.35	$60.40
Purchase #2	$128.84	12.479%	$144.9179	$144.92	$144.90	$144.90
Purchase #3	$98.72	4.124%	$102.7912	$102.79	$102.80	$102.80
Purchase #4	$192.70	8.411%	$208.908	$208.91	$208.90	$208.90
Purchase #5	$38.92	3.584%	$40.3149	$40.31	$40.30	$40.30
Purchase #6	$64.47	10.596%	$71.3012	$71.30	$71.30	$71.30
Purchase #7	$63.28	13.513%	$71.831	$71.83	$71.85	$71.80
7 purchase totals =	$640.20		$700.4244	$700.42	$700.40	$700.40