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	$8.54	11.542%	$9.5257	$9.53	$9.55	$9.50
Purchase #2	$158.72	12.233%	$178.1362	$178.14	$178.15	$178.10
Purchase #3	$50.63	12.306%	$56.8605	$56.86	$56.85	$56.90
Purchase #4	$202.76	9.229%	$221.4727	$221.47	$221.45	$221.50
Purchase #5	$103.90	7.104%	$111.2811	$111.28	$111.30	$111.30
Purchase #6	$52.68	13.627%	$59.8587	$59.86	$59.85	$59.90
Purchase #7	$102.31	9.556%	$112.0867	$112.09	$112.10	$112.10
7 purchase totals =	$679.54		$749.2216	$749.23	$749.25	$749.30