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	$236.69	9.585%	$259.3767	$259.38	$259.40	$259.40
Purchase #2	$91.65	13.538%	$104.0576	$104.06	$104.05	$104.10
Purchase #3	$204.54	9.765%	$224.5133	$224.51	$224.50	$224.50
Purchase #4	$93.98	5.867%	$99.4938	$99.49	$99.50	$99.50
Purchase #5	$29.91	6.716%	$31.9188	$31.92	$31.90	$31.90
Purchase #6	$206.82	9.354%	$226.1659	$226.17	$226.15	$226.20
Purchase #7	$55.84	5.780%	$59.0676	$59.07	$59.05	$59.10
7 purchase totals =	$919.43		$1,004.5937	$1,004.60	$1,004.55	$1,004.70