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	$56.48	6.156%	$59.9569	$59.96	$59.95	$60.00
Purchase #2	$46.59	5.137%	$48.9833	$48.98	$49.00	$49.00
Purchase #3	$169.53	5.655%	$179.1169	$179.12	$179.10	$179.10
Purchase #4	$161.43	3.145%	$166.507	$166.51	$166.50	$166.50
Purchase #5	$169.44	13.610%	$192.5008	$192.50	$192.50	$192.50
Purchase #6	$192.55	13.286%	$218.1322	$218.13	$218.15	$218.10
Purchase #7	$72.76	6.372%	$77.3963	$77.40	$77.40	$77.40
7 purchase totals =	$868.78		$942.5934	$942.60	$942.60	$942.60