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	$47.39	6.556%	$50.4969	$50.50	$50.50	$50.50
Purchase #2	$182.63	4.278%	$190.4429	$190.44	$190.45	$190.40
Purchase #3	$139.70	4.624%	$146.1597	$146.16	$146.15	$146.20
Purchase #4	$89.66	4.707%	$93.8803	$93.88	$93.90	$93.90
Purchase #5	$77.77	10.482%	$85.9219	$85.92	$85.90	$85.90
Purchase #6	$45.41	3.843%	$47.1551	$47.16	$47.15	$47.20
Purchase #7	$207.83	12.303%	$233.3993	$233.40	$233.40	$233.40
7 purchase totals =	$790.39		$847.4561	$847.46	$847.45	$847.50