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	$221.82	9.119%	$242.0478	$242.05	$242.05	$242.00
Purchase #2	$121.92	5.431%	$128.5415	$128.54	$128.55	$128.50
Purchase #3	$35.99	12.417%	$40.4589	$40.46	$40.45	$40.50
Purchase #4	$129.46	9.349%	$141.5632	$141.56	$141.55	$141.60
Purchase #5	$139.51	4.459%	$145.7308	$145.73	$145.75	$145.70
Purchase #6	$211.32	10.622%	$233.7664	$233.77	$233.75	$233.80
Purchase #7	$58.78	11.688%	$65.6502	$65.65	$65.65	$65.70
7 purchase totals =	$918.80		$997.7588	$997.76	$997.75	$997.80