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	$101.92	7.415%	$109.4774	$109.48	$109.50	$109.50
Purchase #2	$65.97	9.711%	$72.3763	$72.38	$72.40	$72.40
Purchase #3	$90.45	9.754%	$99.2725	$99.27	$99.25	$99.30
Purchase #4	$242.99	10.502%	$268.5088	$268.51	$268.50	$268.50
Purchase #5	$49.86	7.551%	$53.6249	$53.62	$53.60	$53.60
Purchase #6	$188.39	4.765%	$197.3668	$197.37	$197.35	$197.40
Purchase #7	$211.86	3.683%	$219.6628	$219.66	$219.65	$219.70
7 purchase totals =	$951.44		$1,020.2895	$1,020.29	$1,020.25	$1,020.40