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	$159.32	8.391%	$172.6885	$172.69	$172.70	$172.70
Purchase #2	$80.97	6.299%	$86.0703	$86.07	$86.05	$86.10
Purchase #3	$123.26	3.215%	$127.2228	$127.22	$127.20	$127.20
Purchase #4	$73.78	12.175%	$82.7627	$82.76	$82.75	$82.80
Purchase #5	$224.28	13.465%	$254.4793	$254.48	$254.50	$254.50
Purchase #6	$65.82	7.178%	$70.5446	$70.54	$70.55	$70.50
Purchase #7	$72.96	7.133%	$78.1642	$78.16	$78.15	$78.20
7 purchase totals =	$800.39		$871.9324	$871.92	$871.90	$872.00