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	$184.25	3.842%	$191.3289	$191.33	$191.35	$191.30
Purchase #2	$132.90	11.486%	$148.1649	$148.16	$148.15	$148.20
Purchase #3	$91.73	9.132%	$100.1068	$100.11	$100.10	$100.10
Purchase #4	$57.74	11.336%	$64.2854	$64.29	$64.30	$64.30
Purchase #5	$104.65	12.744%	$117.9866	$117.99	$118.00	$118.00
Purchase #6	$203.87	5.760%	$215.6129	$215.61	$215.60	$215.60
Purchase #7	$70.83	10.745%	$78.4407	$78.44	$78.45	$78.40
7 purchase totals =	$845.97		$915.9262	$915.93	$915.95	$915.90