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	$165.48	4.321%	$172.6304	$172.63	$172.65	$172.60
Purchase #2	$81.56	10.796%	$90.3652	$90.37	$90.35	$90.40
Purchase #3	$171.50	7.382%	$184.1601	$184.16	$184.15	$184.20
Purchase #4	$60.62	5.432%	$63.9129	$63.91	$63.90	$63.90
Purchase #5	$39.76	7.397%	$42.701	$42.70	$42.70	$42.70
Purchase #6	$65.66	10.869%	$72.7966	$72.80	$72.80	$72.80
Purchase #7	$182.52	3.210%	$188.3789	$188.38	$188.40	$188.40
7 purchase totals =	$767.10		$814.9451	$814.95	$814.95	$815.00