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	$220.48	6.476%	$234.7583	$234.76	$234.75	$234.80
Purchase #2	$87.94	13.829%	$100.1012	$100.10	$100.10	$100.10
Purchase #3	$130.28	11.412%	$145.1476	$145.15	$145.15	$145.10
Purchase #4	$223.50	8.384%	$242.2382	$242.24	$242.25	$242.20
Purchase #5	$206.53	8.367%	$223.8104	$223.81	$223.80	$223.80
Purchase #6	$88.71	3.429%	$91.7519	$91.75	$91.75	$91.80
Purchase #7	$42.34	3.874%	$43.9803	$43.98	$44.00	$44.00
7 purchase totals =	$999.78		$1,081.7879	$1,081.79	$1,081.80	$1,081.80