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	$119.67	3.229%	$123.5341	$123.53	$123.55	$123.50
Purchase #2	$113.32	6.504%	$120.6903	$120.69	$120.70	$120.70
Purchase #3	$88.86	8.655%	$96.5508	$96.55	$96.55	$96.60
Purchase #4	$178.80	13.746%	$203.3778	$203.38	$203.40	$203.40
Purchase #5	$66.72	7.472%	$71.7053	$71.71	$71.70	$71.70
Purchase #6	$86.42	4.564%	$90.3642	$90.36	$90.35	$90.40
Purchase #7	$187.42	11.234%	$208.4748	$208.47	$208.45	$208.50
7 purchase totals =	$841.21		$914.6973	$914.69	$914.70	$914.80