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	$75.62	12.772%	$85.2782	$85.28	$85.30	$85.30
Purchase #2	$124.72	6.566%	$132.9091	$132.91	$132.90	$132.90
Purchase #3	$224.44	9.217%	$245.1266	$245.13	$245.15	$245.10
Purchase #4	$178.89	11.206%	$198.9364	$198.94	$198.95	$198.90
Purchase #5	$93.31	3.833%	$96.8866	$96.89	$96.90	$96.90
Purchase #6	$221.90	4.195%	$231.2087	$231.21	$231.20	$231.20
Purchase #7	$81.57	11.220%	$90.7222	$90.72	$90.70	$90.70
7 purchase totals =	$1,000.45		$1,081.0678	$1,081.08	$1,081.10	$1,081.00