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	$228.89	8.584%	$248.5379	$248.54	$248.55	$248.50
Purchase #2	$151.84	3.818%	$157.6373	$157.64	$157.65	$157.60
Purchase #3	$80.54	12.223%	$90.3844	$90.38	$90.40	$90.40
Purchase #4	$217.83	7.173%	$233.4549	$233.45	$233.45	$233.50
Purchase #5	$125.55	9.331%	$137.2651	$137.27	$137.25	$137.30
Purchase #6	$64.66	12.322%	$72.6274	$72.63	$72.65	$72.60
Purchase #7	$105.29	13.451%	$119.4526	$119.45	$119.45	$119.50
7 purchase totals =	$974.60		$1,059.3596	$1,059.36	$1,059.40	$1,059.40