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	$94.63	10.420%	$104.4904	$104.49	$104.50	$104.50
Purchase #2	$222.94	7.554%	$239.7809	$239.78	$239.80	$239.80
Purchase #3	$73.79	4.722%	$77.2744	$77.27	$77.25	$77.30
Purchase #4	$101.36	4.142%	$105.5583	$105.56	$105.55	$105.60
Purchase #5	$126.93	5.225%	$133.5621	$133.56	$133.55	$133.60
Purchase #6	$48.93	10.164%	$53.9032	$53.90	$53.90	$53.90
Purchase #7	$243.74	9.321%	$266.459	$266.46	$266.45	$266.50
7 purchase totals =	$912.32		$981.0283	$981.02	$981.00	$981.20