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	$213.82	5.195%	$224.9279	$224.93	$224.95	$224.90
Purchase #2	$123.48	13.200%	$139.7794	$139.78	$139.80	$139.80
Purchase #3	$56.65	4.571%	$59.2395	$59.24	$59.25	$59.20
Purchase #4	$40.73	4.322%	$42.4904	$42.49	$42.50	$42.50
Purchase #5	$179.89	11.234%	$200.0988	$200.10	$200.10	$200.10
Purchase #6	$215.75	3.739%	$223.8169	$223.82	$223.80	$223.80
Purchase #7	$100.74	4.256%	$105.0275	$105.03	$105.05	$105.00
7 purchase totals =	$931.06		$995.3804	$995.39	$995.45	$995.30