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	$103.33	5.816%	$109.3397	$109.34	$109.35	$109.30
Purchase #2	$127.51	10.282%	$140.6206	$140.62	$140.60	$140.60
Purchase #3	$43.95	10.441%	$48.5388	$48.54	$48.55	$48.50
Purchase #4	$58.28	7.560%	$62.686	$62.69	$62.70	$62.70
Purchase #5	$40.30	10.804%	$44.654	$44.65	$44.65	$44.70
Purchase #6	$17.50	3.844%	$18.1727	$18.17	$18.15	$18.20
Purchase #7	$168.98	13.178%	$191.2482	$191.25	$191.25	$191.20
7 purchase totals =	$559.85		$615.2600	$615.26	$615.25	$615.20