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	$165.69	10.131%	$182.4761	$182.48	$182.50	$182.50
Purchase #2	$117.70	8.837%	$128.1011	$128.10	$128.10	$128.10
Purchase #3	$210.80	13.597%	$239.4625	$239.46	$239.45	$239.50
Purchase #4	$88.96	13.241%	$100.7392	$100.74	$100.75	$100.70
Purchase #5	$81.61	11.296%	$90.8287	$90.83	$90.85	$90.80
Purchase #6	$150.77	7.121%	$161.5063	$161.51	$161.50	$161.50
Purchase #7	$110.31	5.214%	$116.0616	$116.06	$116.05	$116.10
7 purchase totals =	$925.84		$1,019.1755	$1,019.18	$1,019.20	$1,019.20