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	$32.51	11.820%	$36.3527	$36.35	$36.35	$36.40
Purchase #2	$81.50	10.332%	$89.9206	$89.92	$89.90	$89.90
Purchase #3	$124.67	12.587%	$140.3622	$140.36	$140.35	$140.40
Purchase #4	$127.87	9.578%	$140.1174	$140.12	$140.10	$140.10
Purchase #5	$88.84	6.228%	$94.373	$94.37	$94.35	$94.40
Purchase #6	$250.27	11.719%	$279.5991	$279.60	$279.60	$279.60
Purchase #7	$214.27	13.271%	$242.7058	$242.71	$242.70	$242.70
7 purchase totals =	$919.93		$1,023.4308	$1,023.43	$1,023.35	$1,023.50