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	$129.76	11.253%	$144.3619	$144.36	$144.35	$144.40
Purchase #2	$234.94	12.336%	$263.9222	$263.92	$263.90	$263.90
Purchase #3	$92.98	4.141%	$96.8303	$96.83	$96.85	$96.80
Purchase #4	$95.38	4.668%	$99.8323	$99.83	$99.85	$99.80
Purchase #5	$198.45	6.640%	$211.6271	$211.63	$211.65	$211.60
Purchase #6	$38.60	10.364%	$42.6005	$42.60	$42.60	$42.60
Purchase #7	$35.92	6.656%	$38.3108	$38.31	$38.30	$38.30
7 purchase totals =	$826.03		$897.4851	$897.48	$897.50	$897.40