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	$75.26	7.765%	$81.1039	$81.10	$81.10	$81.10
Purchase #2	$55.61	7.552%	$59.8097	$59.81	$59.80	$59.80
Purchase #3	$42.75	13.767%	$48.6354	$48.64	$48.65	$48.60
Purchase #4	$164.43	9.113%	$179.4145	$179.41	$179.40	$179.40
Purchase #5	$96.43	3.422%	$99.7298	$99.73	$99.75	$99.70
Purchase #6	$214.49	11.334%	$238.8003	$238.80	$238.80	$238.80
Purchase #7	$246.59	7.307%	$264.6083	$264.61	$264.60	$264.60
7 purchase totals =	$895.56		$972.1019	$972.10	$972.10	$972.00