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	$31.56	7.177%	$33.8251	$33.83	$33.85	$33.80
Purchase #2	$224.43	6.476%	$238.9641	$238.96	$238.95	$239.00
Purchase #3	$184.31	6.554%	$196.3897	$196.39	$196.40	$196.40
Purchase #4	$169.84	13.412%	$192.6189	$192.62	$192.60	$192.60
Purchase #5	$207.62	12.226%	$233.0036	$233.00	$233.00	$233.00
Purchase #6	$130.65	4.870%	$137.0127	$137.01	$137.00	$137.00
Purchase #7	$40.98	11.263%	$45.5956	$45.60	$45.60	$45.60
7 purchase totals =	$989.39		$1,077.4097	$1,077.41	$1,077.40	$1,077.40