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	$178.83	4.264%	$186.4553	$186.46	$186.45	$186.50
Purchase #2	$130.83	13.279%	$148.2029	$148.20	$148.20	$148.20
Purchase #3	$148.66	4.523%	$155.3839	$155.38	$155.40	$155.40
Purchase #4	$69.72	13.660%	$79.2438	$79.24	$79.25	$79.20
Purchase #5	$42.67	6.696%	$45.5272	$45.53	$45.55	$45.50
Purchase #6	$127.88	7.239%	$137.1372	$137.14	$137.15	$137.10
Purchase #7	$193.86	9.295%	$211.8793	$211.88	$211.90	$211.90
7 purchase totals =	$892.45		$963.8296	$963.83	$963.90	$963.80