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	$122.30	4.565%	$127.883	$127.88	$127.90	$127.90
Purchase #2	$207.56	4.172%	$216.2194	$216.22	$216.20	$216.20
Purchase #3	$6.93	10.269%	$7.6416	$7.64	$7.65	$7.60
Purchase #4	$120.41	9.130%	$131.4034	$131.40	$131.40	$131.40
Purchase #5	$137.74	4.844%	$144.4121	$144.41	$144.40	$144.40
Purchase #6	$57.82	9.765%	$63.4661	$63.47	$63.45	$63.50
Purchase #7	$7.37	7.413%	$7.9163	$7.92	$7.90	$7.90
7 purchase totals =	$660.13		$698.9419	$698.94	$698.90	$698.90