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	$33.33	8.457%	$36.1487	$36.15	$36.15	$36.10
Purchase #2	$224.86	9.719%	$246.7141	$246.71	$246.70	$246.70
Purchase #3	$88.64	13.758%	$100.8351	$100.84	$100.85	$100.80
Purchase #4	$50.53	7.626%	$54.3834	$54.38	$54.40	$54.40
Purchase #5	$88.82	10.601%	$98.2358	$98.24	$98.25	$98.20
Purchase #6	$25.43	13.585%	$28.8847	$28.88	$28.90	$28.90
Purchase #7	$126.49	4.216%	$131.8228	$131.82	$131.80	$131.80
7 purchase totals =	$638.10		$697.0246	$697.02	$697.05	$696.90