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	$160.33	3.805%	$166.4306	$166.43	$166.45	$166.40
Purchase #2	$30.38	3.564%	$31.4627	$31.46	$31.45	$31.50
Purchase #3	$111.60	3.663%	$115.6879	$115.69	$115.70	$115.70
Purchase #4	$108.49	10.149%	$119.5007	$119.50	$119.50	$119.50
Purchase #5	$63.37	12.222%	$71.1151	$71.12	$71.10	$71.10
Purchase #6	$117.26	11.818%	$131.1178	$131.12	$131.10	$131.10
Purchase #7	$164.32	8.658%	$178.5468	$178.55	$178.55	$178.50
7 purchase totals =	$755.75		$813.8616	$813.87	$813.85	$813.80