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	$99.99	3.419%	$103.4087	$103.41	$103.40	$103.40
Purchase #2	$40.50	9.403%	$44.3082	$44.31	$44.30	$44.30
Purchase #3	$115.50	5.242%	$121.5545	$121.55	$121.55	$121.60
Purchase #4	$109.53	9.627%	$120.0745	$120.07	$120.05	$120.10
Purchase #5	$186.43	5.526%	$196.7321	$196.73	$196.75	$196.70
Purchase #6	$166.91	13.163%	$188.8804	$188.88	$188.90	$188.90
Purchase #7	$127.62	9.301%	$139.4899	$139.49	$139.50	$139.50
7 purchase totals =	$846.48		$914.4483	$914.44	$914.45	$914.50