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	$12.80	7.747%	$13.7916	$13.79	$13.80	$13.80
Purchase #2	$114.67	13.818%	$130.5151	$130.52	$130.50	$130.50
Purchase #3	$36.67	9.769%	$40.2523	$40.25	$40.25	$40.30
Purchase #4	$90.93	9.120%	$99.2228	$99.22	$99.20	$99.20
Purchase #5	$107.34	12.206%	$120.4419	$120.44	$120.45	$120.40
Purchase #6	$39.25	3.347%	$40.5637	$40.56	$40.55	$40.60
Purchase #7	$77.87	3.196%	$80.3587	$80.36	$80.35	$80.40
7 purchase totals =	$479.53		$525.1461	$525.14	$525.10	$525.20