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	$78.92	13.191%	$89.3303	$89.33	$89.35	$89.30
Purchase #2	$21.83	6.437%	$23.2352	$23.24	$23.25	$23.20
Purchase #3	$99.51	9.536%	$108.9993	$109.00	$109.00	$109.00
Purchase #4	$78.73	13.594%	$89.4326	$89.43	$89.45	$89.40
Purchase #5	$94.37	3.618%	$97.7843	$97.78	$97.80	$97.80
Purchase #6	$76.89	4.473%	$80.3293	$80.33	$80.35	$80.30
Purchase #7	$12.39	9.559%	$13.5744	$13.57	$13.55	$13.60
7 purchase totals =	$462.64		$502.6854	$502.68	$502.75	$502.60