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	$138.81	7.233%	$148.8501	$148.85	$148.85	$148.90
Purchase #2	$124.56	6.740%	$132.9553	$132.96	$132.95	$133.00
Purchase #3	$239.81	12.568%	$269.9493	$269.95	$269.95	$269.90
Purchase #4	$125.56	4.777%	$131.558	$131.56	$131.55	$131.60
Purchase #5	$221.50	9.293%	$242.084	$242.08	$242.10	$242.10
Purchase #6	$83.77	6.401%	$89.1321	$89.13	$89.15	$89.10
Purchase #7	$11.74	4.747%	$12.2973	$12.30	$12.30	$12.30
7 purchase totals =	$945.75		$1,026.8261	$1,026.83	$1,026.85	$1,026.90