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	$6.98	11.573%	$7.7878	$7.79	$7.80	$7.80
Purchase #2	$96.49	11.348%	$107.4397	$107.44	$107.45	$107.40
Purchase #3	$127.29	11.571%	$142.0187	$142.02	$142.00	$142.00
Purchase #4	$110.75	11.854%	$123.8783	$123.88	$123.90	$123.90
Purchase #5	$31.35	4.819%	$32.8608	$32.86	$32.85	$32.90
Purchase #6	$96.77	9.480%	$105.9438	$105.94	$105.95	$105.90
Purchase #7	$76.99	6.336%	$81.8681	$81.87	$81.85	$81.90
7 purchase totals =	$546.62		$601.7972	$601.80	$601.80	$601.80