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	$155.94	13.828%	$177.5034	$177.50	$177.50	$177.50
Purchase #2	$99.48	6.491%	$105.9372	$105.94	$105.95	$105.90
Purchase #3	$145.32	13.813%	$165.3931	$165.39	$165.40	$165.40
Purchase #4	$191.94	4.623%	$200.8134	$200.81	$200.80	$200.80
Purchase #5	$153.72	13.406%	$174.3277	$174.33	$174.35	$174.30
Purchase #6	$73.95	10.729%	$81.8841	$81.88	$81.90	$81.90
Purchase #7	$69.84	10.515%	$77.1837	$77.18	$77.20	$77.20
7 purchase totals =	$890.19		$983.0426	$983.03	$983.10	$983.00