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	$79.89	3.768%	$82.9003	$82.90	$82.90	$82.90
Purchase #2	$138.36	12.380%	$155.489	$155.49	$155.50	$155.50
Purchase #3	$79.30	3.254%	$81.8804	$81.88	$81.90	$81.90
Purchase #4	$64.39	10.502%	$71.1522	$71.15	$71.15	$71.20
Purchase #5	$240.60	7.537%	$258.734	$258.73	$258.75	$258.70
Purchase #6	$233.85	13.767%	$266.0441	$266.04	$266.05	$266.00
Purchase #7	$104.56	4.324%	$109.0812	$109.08	$109.10	$109.10
7 purchase totals =	$940.95		$1,025.2812	$1,025.27	$1,025.35	$1,025.30