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	$9.67	6.120%	$10.2618	$10.26	$10.25	$10.30
Purchase #2	$80.80	12.842%	$91.1763	$91.18	$91.20	$91.20
Purchase #3	$64.76	9.745%	$71.0709	$71.07	$71.05	$71.10
Purchase #4	$117.85	8.736%	$128.1454	$128.15	$128.15	$128.10
Purchase #5	$143.89	10.383%	$158.8301	$158.83	$158.85	$158.80
Purchase #6	$93.34	10.279%	$102.9344	$102.93	$102.95	$102.90
Purchase #7	$182.28	4.702%	$190.8508	$190.85	$190.85	$190.90
7 purchase totals =	$692.59		$753.2697	$753.27	$753.30	$753.30