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	$54.60	8.234%	$59.0958	$59.10	$59.10	$59.10
Purchase #2	$41.81	11.825%	$46.754	$46.75	$46.75	$46.80
Purchase #3	$141.94	9.222%	$155.0297	$155.03	$155.05	$155.00
Purchase #4	$181.49	10.475%	$200.5011	$200.50	$200.50	$200.50
Purchase #5	$120.78	4.814%	$126.5943	$126.59	$126.60	$126.60
Purchase #6	$42.49	7.730%	$45.7745	$45.77	$45.75	$45.80
Purchase #7	$28.84	11.523%	$32.1632	$32.16	$32.15	$32.20
7 purchase totals =	$611.95		$665.9126	$665.90	$665.90	$666.00