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	$107.68	12.646%	$121.2972	$121.30	$121.30	$121.30
Purchase #2	$53.49	11.818%	$59.8114	$59.81	$59.80	$59.80
Purchase #3	$32.31	5.253%	$34.0072	$34.01	$34.00	$34.00
Purchase #4	$89.72	10.413%	$99.0625	$99.06	$99.05	$99.10
Purchase #5	$129.92	13.418%	$147.3527	$147.35	$147.35	$147.40
Purchase #6	$24.94	9.573%	$27.3275	$27.33	$27.35	$27.30
Purchase #7	$107.47	4.566%	$112.3771	$112.38	$112.40	$112.40
7 purchase totals =	$545.53		$601.2356	$601.24	$601.25	$601.30