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	$78.80	13.218%	$89.2158	$89.22	$89.20	$89.20
Purchase #2	$161.54	9.869%	$177.4824	$177.48	$177.50	$177.50
Purchase #3	$238.72	11.567%	$266.3327	$266.33	$266.35	$266.30
Purchase #4	$201.69	4.626%	$211.0202	$211.02	$211.00	$211.00
Purchase #5	$97.61	13.822%	$111.1017	$111.10	$111.10	$111.10
Purchase #6	$107.51	8.283%	$116.4151	$116.42	$116.40	$116.40
Purchase #7	$236.91	12.760%	$267.1397	$267.14	$267.15	$267.10
7 purchase totals =	$1,122.78		$1,238.7076	$1,238.71	$1,238.70	$1,238.60