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	$51.66	9.335%	$56.4825	$56.48	$56.50	$56.50
Purchase #2	$139.46	9.319%	$152.4563	$152.46	$152.45	$152.50
Purchase #3	$54.69	10.360%	$60.3559	$60.36	$60.35	$60.40
Purchase #4	$246.66	9.469%	$270.0162	$270.02	$270.00	$270.00
Purchase #5	$90.40	5.138%	$95.0448	$95.04	$95.05	$95.00
Purchase #6	$59.71	12.626%	$67.249	$67.25	$67.25	$67.20
Purchase #7	$176.71	12.310%	$198.463	$198.46	$198.45	$198.50
7 purchase totals =	$819.29		$900.0677	$900.07	$900.05	$900.10