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	$51.70	4.612%	$54.0844	$54.08	$54.10	$54.10
Purchase #2	$23.47	9.455%	$25.6891	$25.69	$25.70	$25.70
Purchase #3	$119.74	9.133%	$130.6759	$130.68	$130.70	$130.70
Purchase #4	$95.51	4.352%	$99.6666	$99.67	$99.65	$99.70
Purchase #5	$65.47	8.700%	$71.1659	$71.17	$71.15	$71.20
Purchase #6	$96.69	10.106%	$106.4615	$106.46	$106.45	$106.50
Purchase #7	$187.70	4.573%	$196.2835	$196.28	$196.30	$196.30
7 purchase totals =	$640.28		$684.0269	$684.03	$684.05	$684.20