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	$6.96	12.128%	$7.8041	$7.80	$7.80	$7.80
Purchase #2	$161.79	7.796%	$174.4031	$174.40	$174.40	$174.40
Purchase #3	$52.78	12.485%	$59.3696	$59.37	$59.35	$59.40
Purchase #4	$214.69	3.617%	$222.4553	$222.46	$222.45	$222.50
Purchase #5	$52.52	8.447%	$56.9564	$56.96	$56.95	$57.00
Purchase #6	$79.78	6.735%	$85.1532	$85.15	$85.15	$85.20
Purchase #7	$166.56	7.751%	$179.4701	$179.47	$179.45	$179.50
7 purchase totals =	$735.08		$785.6118	$785.61	$785.55	$785.80