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	$17.98	10.715%	$19.9066	$19.91	$19.90	$19.90
Purchase #2	$186.47	5.427%	$196.5897	$196.59	$196.60	$196.60
Purchase #3	$152.70	6.310%	$162.3354	$162.34	$162.35	$162.30
Purchase #4	$241.82	3.811%	$251.0358	$251.04	$251.05	$251.00
Purchase #5	$153.52	11.791%	$171.6215	$171.62	$171.60	$171.60
Purchase #6	$185.51	10.694%	$205.3484	$205.35	$205.35	$205.30
Purchase #7	$210.31	5.229%	$221.3071	$221.31	$221.30	$221.30
7 purchase totals =	$1,148.31		$1,228.1445	$1,228.16	$1,228.15	$1,228.00