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	$123.91	5.595%	$130.8428	$130.84	$130.85	$130.80
Purchase #2	$168.68	13.149%	$190.8597	$190.86	$190.85	$190.90
Purchase #3	$216.77	7.168%	$232.3081	$232.31	$232.30	$232.30
Purchase #4	$44.33	10.215%	$48.8583	$48.86	$48.85	$48.90
Purchase #5	$85.94	9.166%	$93.8173	$93.82	$93.80	$93.80
Purchase #6	$123.31	11.758%	$137.8088	$137.81	$137.80	$137.80
Purchase #7	$116.75	13.390%	$132.3828	$132.38	$132.40	$132.40
7 purchase totals =	$879.69		$966.8778	$966.88	$966.85	$966.90