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	$79.88	4.241%	$83.2677	$83.27	$83.25	$83.30
Purchase #2	$151.72	5.152%	$159.5366	$159.54	$159.55	$159.50
Purchase #3	$6.28	12.370%	$7.0568	$7.06	$7.05	$7.10
Purchase #4	$196.37	13.765%	$223.4003	$223.40	$223.40	$223.40
Purchase #5	$145.80	4.564%	$152.4543	$152.45	$152.45	$152.50
Purchase #6	$157.66	13.813%	$179.4376	$179.44	$179.45	$179.40
Purchase #7	$44.67	10.411%	$49.3206	$49.32	$49.30	$49.30
7 purchase totals =	$782.38		$854.4739	$854.48	$854.45	$854.50