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	$13.59	9.744%	$14.9142	$14.91	$14.90	$14.90
Purchase #2	$118.45	4.208%	$123.4344	$123.43	$123.45	$123.40
Purchase #3	$101.53	4.176%	$105.7699	$105.77	$105.75	$105.80
Purchase #4	$235.61	13.544%	$267.521	$267.52	$267.50	$267.50
Purchase #5	$92.52	7.235%	$99.2138	$99.21	$99.20	$99.20
Purchase #6	$27.68	12.427%	$31.1198	$31.12	$31.10	$31.10
Purchase #7	$145.56	11.221%	$161.8933	$161.89	$161.90	$161.90
7 purchase totals =	$734.94		$803.8664	$803.85	$803.80	$803.80