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	$137.78	6.404%	$146.6034	$146.60	$146.60	$146.60
Purchase #2	$238.71	12.581%	$268.7421	$268.74	$268.75	$268.70
Purchase #3	$186.56	3.138%	$192.4143	$192.41	$192.40	$192.40
Purchase #4	$63.41	10.550%	$70.0998	$70.10	$70.10	$70.10
Purchase #5	$42.46	6.868%	$45.3762	$45.38	$45.40	$45.40
Purchase #6	$127.80	4.682%	$133.7836	$133.78	$133.80	$133.80
Purchase #7	$74.45	10.565%	$82.3156	$82.32	$82.30	$82.30
7 purchase totals =	$871.17		$939.3350	$939.33	$939.35	$939.30