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	$170.90	5.727%	$180.6874	$180.69	$180.70	$180.70
Purchase #2	$99.30	4.528%	$103.7963	$103.80	$103.80	$103.80
Purchase #3	$52.95	8.351%	$57.3719	$57.37	$57.35	$57.40
Purchase #4	$90.72	4.829%	$95.1009	$95.10	$95.10	$95.10
Purchase #5	$84.87	6.309%	$90.2244	$90.22	$90.20	$90.20
Purchase #6	$202.73	6.419%	$215.7432	$215.74	$215.75	$215.70
Purchase #7	$181.37	13.360%	$205.601	$205.60	$205.60	$205.60
7 purchase totals =	$882.84		$948.5251	$948.52	$948.50	$948.50