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	$105.73	12.154%	$118.5804	$118.58	$118.60	$118.60
Purchase #2	$104.90	5.259%	$110.4167	$110.42	$110.40	$110.40
Purchase #3	$109.37	8.472%	$118.6358	$118.64	$118.65	$118.60
Purchase #4	$105.81	5.744%	$111.8877	$111.89	$111.90	$111.90
Purchase #5	$104.65	8.395%	$113.4354	$113.44	$113.45	$113.40
Purchase #6	$53.30	13.648%	$60.5744	$60.57	$60.55	$60.60
Purchase #7	$201.75	3.552%	$208.9162	$208.92	$208.90	$208.90
7 purchase totals =	$785.51		$842.4466	$842.46	$842.45	$842.40