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	$235.94	12.802%	$266.145	$266.15	$266.15	$266.10
Purchase #2	$27.97	13.375%	$31.711	$31.71	$31.70	$31.70
Purchase #3	$69.81	3.504%	$72.2561	$72.26	$72.25	$72.30
Purchase #4	$152.48	13.379%	$172.8803	$172.88	$172.90	$172.90
Purchase #5	$98.69	6.839%	$105.4394	$105.44	$105.45	$105.40
Purchase #6	$174.36	8.164%	$188.5948	$188.59	$188.60	$188.60
Purchase #7	$137.96	13.328%	$156.3473	$156.35	$156.35	$156.30
7 purchase totals =	$897.21		$993.3739	$993.38	$993.40	$993.30