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	$19.61	4.796%	$20.5505	$20.55	$20.55	$20.60
Purchase #2	$26.98	9.399%	$29.5159	$29.52	$29.50	$29.50
Purchase #3	$83.41	8.537%	$90.5307	$90.53	$90.55	$90.50
Purchase #4	$17.38	9.221%	$18.9826	$18.98	$19.00	$19.00
Purchase #5	$15.51	4.760%	$16.2483	$16.25	$16.25	$16.20
Purchase #6	$99.25	11.665%	$110.8275	$110.83	$110.85	$110.80
Purchase #7	$242.52	3.273%	$250.4577	$250.46	$250.45	$250.50
7 purchase totals =	$504.66		$537.1132	$537.12	$537.15	$537.10