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	$151.63	12.824%	$171.075	$171.08	$171.10	$171.10
Purchase #2	$185.95	6.794%	$198.5834	$198.58	$198.60	$198.60
Purchase #3	$20.73	13.282%	$23.4834	$23.48	$23.50	$23.50
Purchase #4	$89.76	3.486%	$92.889	$92.89	$92.90	$92.90
Purchase #5	$210.25	11.708%	$234.8661	$234.87	$234.85	$234.90
Purchase #6	$30.78	9.745%	$33.7795	$33.78	$33.80	$33.80
Purchase #7	$84.38	6.472%	$89.8411	$89.84	$89.85	$89.80
7 purchase totals =	$773.48		$844.5175	$844.52	$844.60	$844.60