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	$49.71	12.448%	$55.8979	$55.90	$55.90	$55.90
Purchase #2	$200.93	5.189%	$211.3563	$211.36	$211.35	$211.40
Purchase #3	$11.77	10.477%	$13.0031	$13.00	$13.00	$13.00
Purchase #4	$182.80	9.814%	$200.74	$200.74	$200.75	$200.70
Purchase #5	$39.98	13.609%	$45.4209	$45.42	$45.40	$45.40
Purchase #6	$185.33	10.367%	$204.5432	$204.54	$204.55	$204.50
Purchase #7	$52.91	12.549%	$59.5497	$59.55	$59.55	$59.50
7 purchase totals =	$723.43		$790.5111	$790.51	$790.50	$790.40