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	$159.59	9.547%	$174.8261	$174.83	$174.85	$174.80
Purchase #2	$45.54	12.310%	$51.146	$51.15	$51.15	$51.10
Purchase #3	$162.45	5.143%	$170.8048	$170.80	$170.80	$170.80
Purchase #4	$42.26	5.236%	$44.4727	$44.47	$44.45	$44.50
Purchase #5	$40.71	5.344%	$42.8855	$42.89	$42.90	$42.90
Purchase #6	$134.44	8.229%	$145.5031	$145.50	$145.50	$145.50
Purchase #7	$73.70	11.571%	$82.2278	$82.23	$82.25	$82.20
7 purchase totals =	$658.69		$711.8660	$711.87	$711.90	$711.80