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	$55.87	9.444%	$61.1464	$61.15	$61.15	$61.10
Purchase #2	$78.60	11.733%	$87.8221	$87.82	$87.80	$87.80
Purchase #3	$94.40	3.796%	$97.9834	$97.98	$98.00	$98.00
Purchase #4	$54.84	8.681%	$59.6007	$59.60	$59.60	$59.60
Purchase #5	$25.72	8.692%	$27.9556	$27.96	$27.95	$28.00
Purchase #6	$98.41	13.264%	$111.4631	$111.46	$111.45	$111.50
Purchase #7	$52.62	3.660%	$54.5459	$54.55	$54.55	$54.50
7 purchase totals =	$460.46		$500.5172	$500.52	$500.50	$500.50