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	$65.78	11.833%	$73.5637	$73.56	$73.55	$73.60
Purchase #2	$116.99	9.213%	$127.7683	$127.77	$127.75	$127.80
Purchase #3	$229.45	7.860%	$247.4848	$247.48	$247.50	$247.50
Purchase #4	$32.75	13.546%	$37.1863	$37.19	$37.20	$37.20
Purchase #5	$92.25	8.466%	$100.0599	$100.06	$100.05	$100.10
Purchase #6	$189.74	13.711%	$215.7553	$215.76	$215.75	$215.80
Purchase #7	$68.83	6.175%	$73.0803	$73.08	$73.10	$73.10
7 purchase totals =	$795.79		$874.8986	$874.90	$874.90	$875.10