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	$71.42	9.649%	$78.3113	$78.31	$78.30	$78.30
Purchase #2	$177.31	10.764%	$196.3956	$196.40	$196.40	$196.40
Purchase #3	$67.86	9.619%	$74.3875	$74.39	$74.40	$74.40
Purchase #4	$100.85	11.427%	$112.3741	$112.37	$112.35	$112.40
Purchase #5	$103.80	4.751%	$108.7315	$108.73	$108.75	$108.70
Purchase #6	$152.97	5.431%	$161.2778	$161.28	$161.30	$161.30
Purchase #7	$102.39	11.404%	$114.0666	$114.07	$114.05	$114.10
7 purchase totals =	$776.60		$845.5444	$845.55	$845.55	$845.60