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	$111.53	13.632%	$126.7338	$126.73	$126.75	$126.70
Purchase #2	$57.65	6.269%	$61.2641	$61.26	$61.25	$61.30
Purchase #3	$96.75	13.175%	$109.4968	$109.50	$109.50	$109.50
Purchase #4	$243.63	12.765%	$274.7294	$274.73	$274.75	$274.70
Purchase #5	$146.34	11.368%	$162.9759	$162.98	$163.00	$163.00
Purchase #6	$72.83	10.386%	$80.3941	$80.39	$80.40	$80.40
Purchase #7	$111.95	13.636%	$127.2155	$127.22	$127.20	$127.20
7 purchase totals =	$840.68		$942.8096	$942.81	$942.85	$942.80