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	$50.93	8.654%	$55.3375	$55.34	$55.35	$55.30
Purchase #2	$23.72	3.460%	$24.5407	$24.54	$24.55	$24.50
Purchase #3	$167.51	6.798%	$178.8973	$178.90	$178.90	$178.90
Purchase #4	$65.68	5.646%	$69.3883	$69.39	$69.40	$69.40
Purchase #5	$131.59	10.336%	$145.1911	$145.19	$145.20	$145.20
Purchase #6	$79.77	7.646%	$85.8692	$85.87	$85.85	$85.90
Purchase #7	$52.56	10.147%	$57.8933	$57.89	$57.90	$57.90
7 purchase totals =	$571.76		$617.1174	$617.12	$617.15	$617.10