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	$250.52	10.170%	$275.9979	$276.00	$276.00	$276.00
Purchase #2	$74.41	7.859%	$80.2579	$80.26	$80.25	$80.30
Purchase #3	$113.85	8.795%	$123.8631	$123.86	$123.85	$123.90
Purchase #4	$142.71	12.422%	$160.4374	$160.44	$160.45	$160.40
Purchase #5	$55.69	9.769%	$61.1304	$61.13	$61.15	$61.10
Purchase #6	$149.56	13.354%	$169.5322	$169.53	$169.55	$169.50
Purchase #7	$178.84	4.743%	$187.3224	$187.32	$187.30	$187.30
7 purchase totals =	$965.58		$1,058.5413	$1,058.54	$1,058.55	$1,058.50