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	$117.81	9.626%	$129.1504	$129.15	$129.15	$129.20
Purchase #2	$100.34	8.566%	$108.9351	$108.94	$108.95	$108.90
Purchase #3	$170.79	4.504%	$178.4824	$178.48	$178.50	$178.50
Purchase #4	$213.72	9.164%	$233.3053	$233.31	$233.30	$233.30
Purchase #5	$79.39	13.743%	$90.3006	$90.30	$90.30	$90.30
Purchase #6	$181.55	6.238%	$192.8751	$192.88	$192.90	$192.90
Purchase #7	$123.69	8.104%	$133.7138	$133.71	$133.70	$133.70
7 purchase totals =	$987.29		$1,066.7627	$1,066.77	$1,066.80	$1,066.80