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	$174.87	8.588%	$189.8878	$189.89	$189.90	$189.90
Purchase #2	$151.49	12.415%	$170.2975	$170.30	$170.30	$170.30
Purchase #3	$250.47	11.215%	$278.5602	$278.56	$278.55	$278.60
Purchase #4	$155.95	10.193%	$171.846	$171.85	$171.85	$171.80
Purchase #5	$83.83	3.665%	$86.9024	$86.90	$86.90	$86.90
Purchase #6	$161.43	13.716%	$183.5717	$183.57	$183.55	$183.60
Purchase #7	$64.37	4.381%	$67.19	$67.19	$67.20	$67.20
7 purchase totals =	$1,042.41		$1,148.2556	$1,148.26	$1,148.25	$1,148.30