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	$174.97	6.484%	$186.3151	$186.32	$186.30	$186.30
Purchase #2	$114.30	10.722%	$126.5552	$126.56	$126.55	$126.60
Purchase #3	$30.82	4.184%	$32.1095	$32.11	$32.10	$32.10
Purchase #4	$170.51	12.460%	$191.7555	$191.76	$191.75	$191.80
Purchase #5	$169.45	8.812%	$184.3819	$184.38	$184.40	$184.40
Purchase #6	$85.72	3.242%	$88.499	$88.50	$88.50	$88.50
Purchase #7	$49.80	7.514%	$53.542	$53.54	$53.55	$53.50
7 purchase totals =	$795.57		$863.1582	$863.17	$863.15	$863.20