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	$38.85	7.839%	$41.8955	$41.90	$41.90	$41.90
Purchase #2	$62.59	7.104%	$67.0364	$67.04	$67.05	$67.00
Purchase #3	$134.86	12.526%	$151.7526	$151.75	$151.75	$151.80
Purchase #4	$160.85	13.484%	$182.539	$182.54	$182.55	$182.50
Purchase #5	$109.80	7.740%	$118.2985	$118.30	$118.30	$118.30
Purchase #6	$57.88	12.382%	$65.0467	$65.05	$65.05	$65.00
Purchase #7	$203.91	4.363%	$212.8066	$212.81	$212.80	$212.80
7 purchase totals =	$768.74		$839.3753	$839.39	$839.40	$839.30