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	$22.55	11.478%	$25.1383	$25.14	$25.15	$25.10
Purchase #2	$163.89	6.619%	$174.7379	$174.74	$174.75	$174.70
Purchase #3	$94.47	11.856%	$105.6704	$105.67	$105.65	$105.70
Purchase #4	$73.83	5.744%	$78.0708	$78.07	$78.05	$78.10
Purchase #5	$124.29	3.746%	$128.9459	$128.95	$128.95	$128.90
Purchase #6	$85.62	11.150%	$95.1666	$95.17	$95.15	$95.20
Purchase #7	$214.46	3.796%	$222.6009	$222.60	$222.60	$222.60
7 purchase totals =	$779.11		$830.3308	$830.34	$830.30	$830.30