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	$90.89	9.467%	$99.4946	$99.49	$99.50	$99.50
Purchase #2	$55.74	3.150%	$57.4958	$57.50	$57.50	$57.50
Purchase #3	$10.67	12.524%	$12.0063	$12.01	$12.00	$12.00
Purchase #4	$59.37	4.566%	$62.0808	$62.08	$62.10	$62.10
Purchase #5	$65.71	11.138%	$73.0288	$73.03	$73.05	$73.00
Purchase #6	$91.83	9.824%	$100.8514	$100.85	$100.85	$100.90
Purchase #7	$135.33	4.683%	$141.6675	$141.67	$141.65	$141.70
7 purchase totals =	$509.54		$546.6252	$546.63	$546.65	$546.70