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	$48.30	8.529%	$52.4195	$52.42	$52.40	$52.40
Purchase #2	$169.25	11.660%	$188.9846	$188.98	$189.00	$189.00
Purchase #3	$232.79	13.231%	$263.5904	$263.59	$263.60	$263.60
Purchase #4	$84.53	5.504%	$89.1825	$89.18	$89.20	$89.20
Purchase #5	$94.69	4.799%	$99.2342	$99.23	$99.25	$99.20
Purchase #6	$246.32	11.467%	$274.5655	$274.57	$274.55	$274.60
Purchase #7	$32.39	9.296%	$35.401	$35.40	$35.40	$35.40
7 purchase totals =	$908.27		$1,003.3777	$1,003.37	$1,003.40	$1,003.40