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	$213.74	4.774%	$223.9439	$223.94	$223.95	$223.90
Purchase #2	$138.41	5.483%	$145.999	$146.00	$146.00	$146.00
Purchase #3	$54.51	8.813%	$59.314	$59.31	$59.30	$59.30
Purchase #4	$39.58	7.148%	$42.4092	$42.41	$42.40	$42.40
Purchase #5	$20.79	4.778%	$21.7833	$21.78	$21.80	$21.80
Purchase #6	$205.87	4.289%	$214.6998	$214.70	$214.70	$214.70
Purchase #7	$125.83	7.175%	$134.8583	$134.86	$134.85	$134.90
7 purchase totals =	$798.73		$843.0075	$843.00	$843.00	$843.00