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	$81.53	9.517%	$89.2892	$89.29	$89.30	$89.30
Purchase #2	$221.33	3.517%	$229.1142	$229.11	$229.10	$229.10
Purchase #3	$114.71	12.289%	$128.8067	$128.81	$128.80	$128.80
Purchase #4	$159.94	12.401%	$179.7742	$179.77	$179.75	$179.80
Purchase #5	$56.79	3.592%	$58.8299	$58.83	$58.85	$58.80
Purchase #6	$10.99	9.721%	$12.0583	$12.06	$12.05	$12.10
Purchase #7	$122.60	7.294%	$131.5424	$131.54	$131.55	$131.50
7 purchase totals =	$767.89		$829.4149	$829.41	$829.40	$829.40