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	$93.43	12.737%	$105.3302	$105.33	$105.35	$105.30
Purchase #2	$250.85	12.801%	$282.9613	$282.96	$282.95	$283.00
Purchase #3	$39.37	10.620%	$43.5511	$43.55	$43.55	$43.60
Purchase #4	$103.82	4.223%	$108.2043	$108.20	$108.20	$108.20
Purchase #5	$67.80	13.858%	$77.1957	$77.20	$77.20	$77.20
Purchase #6	$248.67	6.105%	$263.8513	$263.85	$263.85	$263.90
Purchase #7	$242.25	12.811%	$273.2846	$273.28	$273.30	$273.30
7 purchase totals =	$1,046.19		$1,154.3785	$1,154.37	$1,154.40	$1,154.50