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	$174.79	6.692%	$186.4869	$186.49	$186.50	$186.50
Purchase #2	$72.87	4.481%	$76.1353	$76.14	$76.15	$76.10
Purchase #3	$89.38	12.497%	$100.5498	$100.55	$100.55	$100.50
Purchase #4	$242.99	11.709%	$271.4417	$271.44	$271.45	$271.40
Purchase #5	$141.89	10.177%	$156.3301	$156.33	$156.35	$156.30
Purchase #6	$35.78	7.327%	$38.4016	$38.40	$38.40	$38.40
Purchase #7	$38.45	11.548%	$42.8902	$42.89	$42.90	$42.90
7 purchase totals =	$796.15		$872.2356	$872.24	$872.30	$872.10