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	$33.77	5.144%	$35.5071	$35.51	$35.50	$35.50
Purchase #2	$35.27	3.431%	$36.4801	$36.48	$36.50	$36.50
Purchase #3	$115.90	11.110%	$128.7765	$128.78	$128.80	$128.80
Purchase #4	$78.25	8.772%	$85.1141	$85.11	$85.10	$85.10
Purchase #5	$38.47	5.343%	$40.5255	$40.53	$40.55	$40.50
Purchase #6	$78.37	6.237%	$83.2579	$83.26	$83.25	$83.30
Purchase #7	$159.86	7.498%	$171.8463	$171.85	$171.85	$171.80
7 purchase totals =	$539.89		$581.5075	$581.52	$581.55	$581.50