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	$62.42	5.490%	$65.8469	$65.85	$65.85	$65.80
Purchase #2	$228.80	13.350%	$259.3448	$259.34	$259.35	$259.30
Purchase #3	$81.45	10.627%	$90.1057	$90.11	$90.10	$90.10
Purchase #4	$35.76	9.874%	$39.2909	$39.29	$39.30	$39.30
Purchase #5	$193.93	13.140%	$219.4124	$219.41	$219.40	$219.40
Purchase #6	$79.42	12.190%	$89.1013	$89.10	$89.10	$89.10
Purchase #7	$82.54	9.535%	$90.4102	$90.41	$90.40	$90.40
7 purchase totals =	$764.32		$853.5122	$853.51	$853.50	$853.40