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	$11.48	6.556%	$12.2326	$12.23	$12.25	$12.20
Purchase #2	$176.75	13.405%	$200.4433	$200.44	$200.45	$200.40
Purchase #3	$115.36	6.814%	$123.2206	$123.22	$123.20	$123.20
Purchase #4	$144.51	13.677%	$164.2746	$164.27	$164.25	$164.30
Purchase #5	$141.27	9.817%	$155.1385	$155.14	$155.15	$155.10
Purchase #6	$76.53	7.534%	$82.2958	$82.30	$82.30	$82.30
Purchase #7	$123.73	3.579%	$128.1583	$128.16	$128.15	$128.20
7 purchase totals =	$789.63		$865.7637	$865.76	$865.75	$865.70