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	$33.98	11.466%	$37.8761	$37.88	$37.90	$37.90
Purchase #2	$31.98	12.239%	$35.894	$35.89	$35.90	$35.90
Purchase #3	$75.79	11.363%	$84.402	$84.40	$84.40	$84.40
Purchase #4	$110.38	12.268%	$123.9214	$123.92	$123.90	$123.90
Purchase #5	$28.31	13.799%	$32.2165	$32.22	$32.20	$32.20
Purchase #6	$76.89	12.396%	$86.4213	$86.42	$86.40	$86.40
Purchase #7	$46.55	6.531%	$49.5902	$49.59	$49.60	$49.60
7 purchase totals =	$403.88		$450.3215	$450.32	$450.30	$450.30