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	$28.73	11.604%	$32.0638	$32.06	$32.05	$32.10
Purchase #2	$51.73	3.744%	$53.6668	$53.67	$53.65	$53.70
Purchase #3	$98.64	10.415%	$108.9134	$108.91	$108.90	$108.90
Purchase #4	$35.68	13.445%	$40.4772	$40.48	$40.50	$40.50
Purchase #5	$172.83	4.458%	$180.5348	$180.53	$180.55	$180.50
Purchase #6	$97.50	12.271%	$109.4642	$109.46	$109.45	$109.50
Purchase #7	$45.63	12.769%	$51.4565	$51.46	$51.45	$51.50
7 purchase totals =	$530.74		$576.5767	$576.57	$576.55	$576.70