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	$79.41	12.868%	$89.6285	$89.63	$89.65	$89.60
Purchase #2	$104.89	3.772%	$108.8465	$108.85	$108.85	$108.80
Purchase #3	$74.88	7.831%	$80.7439	$80.74	$80.75	$80.70
Purchase #4	$55.42	7.181%	$59.3997	$59.40	$59.40	$59.40
Purchase #5	$116.48	7.223%	$124.8934	$124.89	$124.90	$124.90
Purchase #6	$125.29	6.755%	$133.7533	$133.75	$133.75	$133.80
Purchase #7	$19.48	5.225%	$20.4978	$20.50	$20.50	$20.50
7 purchase totals =	$575.85		$617.7631	$617.76	$617.80	$617.70