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	$81.36	10.499%	$89.902	$89.90	$89.90	$89.90
Purchase #2	$62.72	5.119%	$65.9306	$65.93	$65.95	$65.90
Purchase #3	$43.57	13.305%	$49.367	$49.37	$49.35	$49.40
Purchase #4	$77.96	3.520%	$80.7042	$80.70	$80.70	$80.70
Purchase #5	$88.45	13.216%	$100.1396	$100.14	$100.15	$100.10
Purchase #6	$79.89	8.775%	$86.9003	$86.90	$86.90	$86.90
Purchase #7	$191.34	10.696%	$211.8057	$211.81	$211.80	$211.80
7 purchase totals =	$625.29		$684.7494	$684.75	$684.75	$684.70