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	$204.67	5.116%	$215.1409	$215.14	$215.15	$215.10
Purchase #2	$92.74	13.692%	$105.438	$105.44	$105.45	$105.40
Purchase #3	$232.87	5.388%	$245.417	$245.42	$245.40	$245.40
Purchase #4	$55.57	6.744%	$59.3176	$59.32	$59.30	$59.30
Purchase #5	$86.54	12.788%	$97.6067	$97.61	$97.60	$97.60
Purchase #6	$40.41	12.537%	$45.4762	$45.48	$45.50	$45.50
Purchase #7	$163.83	4.391%	$171.0238	$171.02	$171.00	$171.00
7 purchase totals =	$876.63		$939.4202	$939.43	$939.40	$939.30