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	$239.50	6.279%	$254.5382	$254.54	$254.55	$254.50
Purchase #2	$124.90	9.706%	$137.0228	$137.02	$137.00	$137.00
Purchase #3	$154.78	13.658%	$175.9199	$175.92	$175.90	$175.90
Purchase #4	$117.68	10.619%	$130.1764	$130.18	$130.20	$130.20
Purchase #5	$67.51	8.762%	$73.4252	$73.43	$73.45	$73.40
Purchase #6	$69.60	12.145%	$78.0529	$78.05	$78.05	$78.10
Purchase #7	$141.80	10.206%	$156.2721	$156.27	$156.25	$156.30
7 purchase totals =	$915.77		$1,005.4075	$1,005.41	$1,005.40	$1,005.40