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	$206.79	4.128%	$215.3263	$215.33	$215.35	$215.30
Purchase #2	$60.78	13.787%	$69.1597	$69.16	$69.15	$69.20
Purchase #3	$130.55	11.260%	$145.2499	$145.25	$145.25	$145.20
Purchase #4	$130.34	10.151%	$143.5708	$143.57	$143.55	$143.60
Purchase #5	$170.53	8.126%	$184.3873	$184.39	$184.40	$184.40
Purchase #6	$36.89	13.650%	$41.9255	$41.93	$41.95	$41.90
Purchase #7	$85.42	4.260%	$89.0589	$89.06	$89.05	$89.10
7 purchase totals =	$821.30		$888.6784	$888.69	$888.70	$888.70