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	$157.72	4.265%	$164.4468	$164.45	$164.45	$164.40
Purchase #2	$191.36	7.252%	$205.2374	$205.24	$205.25	$205.20
Purchase #3	$85.64	8.119%	$92.5931	$92.59	$92.60	$92.60
Purchase #4	$43.68	8.149%	$47.2395	$47.24	$47.25	$47.20
Purchase #5	$40.51	5.261%	$42.6412	$42.64	$42.65	$42.60
Purchase #6	$82.95	10.765%	$91.8796	$91.88	$91.90	$91.90
Purchase #7	$239.89	3.305%	$247.8184	$247.82	$247.80	$247.80
7 purchase totals =	$841.75		$891.8560	$891.86	$891.90	$891.70