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	$33.87	3.653%	$35.1073	$35.11	$35.10	$35.10
Purchase #2	$242.98	11.181%	$270.1476	$270.15	$270.15	$270.10
Purchase #3	$187.92	6.604%	$200.3302	$200.33	$200.35	$200.30
Purchase #4	$80.51	8.640%	$87.4661	$87.47	$87.45	$87.50
Purchase #5	$34.49	9.698%	$37.8348	$37.83	$37.85	$37.80
Purchase #6	$30.47	11.245%	$33.8964	$33.90	$33.90	$33.90
Purchase #7	$33.48	11.291%	$37.2602	$37.26	$37.25	$37.30
7 purchase totals =	$643.72		$702.0426	$702.05	$702.05	$702.00