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	$127.61	6.352%	$135.7158	$135.72	$135.70	$135.70
Purchase #2	$112.78	9.351%	$123.3261	$123.33	$123.35	$123.30
Purchase #3	$217.78	8.574%	$236.4525	$236.45	$236.45	$236.50
Purchase #4	$81.57	11.425%	$90.8894	$90.89	$90.90	$90.90
Purchase #5	$95.26	12.453%	$107.1227	$107.12	$107.10	$107.10
Purchase #6	$57.25	3.704%	$59.3705	$59.37	$59.35	$59.40
Purchase #7	$166.56	3.130%	$171.7733	$171.77	$171.75	$171.80
7 purchase totals =	$858.81		$924.6503	$924.65	$924.60	$924.70