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	$94.98	4.288%	$99.0527	$99.05	$99.05	$99.10
Purchase #2	$164.38	13.424%	$186.4464	$186.45	$186.45	$186.40
Purchase #3	$152.51	12.519%	$171.6027	$171.60	$171.60	$171.60
Purchase #4	$194.92	7.364%	$209.2739	$209.27	$209.25	$209.30
Purchase #5	$193.78	7.141%	$207.6178	$207.62	$207.60	$207.60
Purchase #6	$160.40	11.856%	$179.417	$179.42	$179.40	$179.40
Purchase #7	$39.95	13.678%	$45.4144	$45.41	$45.40	$45.40
7 purchase totals =	$1,000.92		$1,098.8249	$1,098.82	$1,098.75	$1,098.80