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	$127.42	3.740%	$132.1855	$132.19	$132.20	$132.20
Purchase #2	$55.51	13.119%	$62.7924	$62.79	$62.80	$62.80
Purchase #3	$109.96	6.601%	$117.2185	$117.22	$117.20	$117.20
Purchase #4	$160.39	4.734%	$167.9829	$167.98	$168.00	$168.00
Purchase #5	$53.62	11.200%	$59.6254	$59.63	$59.65	$59.60
Purchase #6	$62.71	7.626%	$67.4923	$67.49	$67.50	$67.50
Purchase #7	$19.78	6.837%	$21.1324	$21.13	$21.15	$21.10
7 purchase totals =	$589.39		$628.4294	$628.43	$628.50	$628.40