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	$48.84	8.122%	$52.8068	$52.81	$52.80	$52.80
Purchase #2	$182.96	7.536%	$196.7479	$196.75	$196.75	$196.70
Purchase #3	$209.67	13.141%	$237.2227	$237.22	$237.20	$237.20
Purchase #4	$116.32	6.411%	$123.7773	$123.78	$123.80	$123.80
Purchase #5	$223.28	5.149%	$234.7767	$234.78	$234.80	$234.80
Purchase #6	$223.90	4.372%	$233.6889	$233.69	$233.70	$233.70
Purchase #7	$243.62	12.278%	$273.5317	$273.53	$273.55	$273.50
7 purchase totals =	$1,248.59		$1,352.5520	$1,352.56	$1,352.60	$1,352.50