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	$124.80	13.250%	$141.336	$141.34	$141.35	$141.30
Purchase #2	$173.70	10.120%	$191.2784	$191.28	$191.30	$191.30
Purchase #3	$36.66	10.273%	$40.4261	$40.43	$40.45	$40.40
Purchase #4	$81.33	10.859%	$90.1616	$90.16	$90.15	$90.20
Purchase #5	$140.93	13.155%	$159.4693	$159.47	$159.45	$159.50
Purchase #6	$90.59	9.289%	$99.0049	$99.00	$99.00	$99.00
Purchase #7	$90.71	7.197%	$97.2384	$97.24	$97.25	$97.20
7 purchase totals =	$738.72		$818.9147	$818.92	$818.95	$818.90