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	$36.52	10.450%	$40.3363	$40.34	$40.35	$40.30
Purchase #2	$250.54	3.166%	$258.4721	$258.47	$258.45	$258.50
Purchase #3	$53.29	10.498%	$58.8844	$58.88	$58.90	$58.90
Purchase #4	$59.37	10.204%	$65.4281	$65.43	$65.45	$65.40
Purchase #5	$234.72	13.704%	$266.886	$266.89	$266.90	$266.90
Purchase #6	$175.77	9.251%	$192.0305	$192.03	$192.05	$192.00
Purchase #7	$151.37	12.318%	$170.0158	$170.02	$170.00	$170.00
7 purchase totals =	$961.58		$1,052.0532	$1,052.06	$1,052.10	$1,052.00