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	$63.75	12.773%	$71.8928	$71.89	$71.90	$71.90
Purchase #2	$54.82	9.185%	$59.8552	$59.86	$59.85	$59.90
Purchase #3	$169.93	5.227%	$178.8122	$178.81	$178.80	$178.80
Purchase #4	$57.63	8.166%	$62.3361	$62.34	$62.35	$62.30
Purchase #5	$63.62	7.820%	$68.5951	$68.60	$68.60	$68.60
Purchase #6	$185.69	3.195%	$191.6228	$191.62	$191.60	$191.60
Purchase #7	$224.97	10.190%	$247.8944	$247.89	$247.90	$247.90
7 purchase totals =	$820.41		$881.0086	$881.01	$881.00	$881.00