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	$30.91	5.662%	$32.6601	$32.66	$32.65	$32.70
Purchase #2	$214.50	3.535%	$222.0826	$222.08	$222.10	$222.10
Purchase #3	$110.73	8.389%	$120.0191	$120.02	$120.00	$120.00
Purchase #4	$240.55	12.190%	$269.873	$269.87	$269.85	$269.90
Purchase #5	$57.35	3.787%	$59.5218	$59.52	$59.50	$59.50
Purchase #6	$91.98	4.181%	$95.8257	$95.83	$95.85	$95.80
Purchase #7	$224.89	6.412%	$239.3099	$239.31	$239.30	$239.30
7 purchase totals =	$970.91		$1,039.2922	$1,039.29	$1,039.25	$1,039.30