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	$36.79	4.112%	$38.3028	$38.30	$38.30	$38.30
Purchase #2	$186.45	7.440%	$200.3219	$200.32	$200.30	$200.30
Purchase #3	$240.29	6.487%	$255.8776	$255.88	$255.90	$255.90
Purchase #4	$114.95	8.601%	$124.8368	$124.84	$124.85	$124.80
Purchase #5	$164.28	11.191%	$182.6646	$182.66	$182.65	$182.70
Purchase #6	$233.38	10.155%	$257.0797	$257.08	$257.10	$257.10
Purchase #7	$108.38	13.691%	$123.2183	$123.22	$123.20	$123.20
7 purchase totals =	$1,084.52		$1,182.3017	$1,182.30	$1,182.30	$1,182.30