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	$100.67	8.751%	$109.4796	$109.48	$109.50	$109.50
Purchase #2	$71.77	10.156%	$79.059	$79.06	$79.05	$79.10
Purchase #3	$71.64	9.439%	$78.4021	$78.40	$78.40	$78.40
Purchase #4	$30.33	6.341%	$32.2532	$32.25	$32.25	$32.30
Purchase #5	$140.67	13.190%	$159.2244	$159.22	$159.20	$159.20
Purchase #6	$21.38	13.419%	$24.249	$24.25	$24.25	$24.20
Purchase #7	$31.77	7.630%	$34.1941	$34.19	$34.20	$34.20
7 purchase totals =	$468.23		$516.8614	$516.85	$516.85	$516.90