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	$235.32	6.620%	$250.8982	$250.90	$250.90	$250.90
Purchase #2	$141.48	9.191%	$154.4834	$154.48	$154.50	$154.50
Purchase #3	$235.99	5.160%	$248.1671	$248.17	$248.15	$248.20
Purchase #4	$5.49	7.479%	$5.9006	$5.90	$5.90	$5.90
Purchase #5	$182.33	9.726%	$200.0634	$200.06	$200.05	$200.10
Purchase #6	$80.33	13.795%	$91.4115	$91.41	$91.40	$91.40
Purchase #7	$183.64	4.208%	$191.3676	$191.37	$191.35	$191.40
7 purchase totals =	$1,064.58		$1,142.2918	$1,142.29	$1,142.25	$1,142.40