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	$239.43	12.403%	$269.1265	$269.13	$269.15	$269.10
Purchase #2	$99.27	11.726%	$110.9104	$110.91	$110.90	$110.90
Purchase #3	$105.65	8.440%	$114.5669	$114.57	$114.55	$114.60
Purchase #4	$141.82	9.665%	$155.5269	$155.53	$155.55	$155.50
Purchase #5	$221.50	13.151%	$250.6295	$250.63	$250.65	$250.60
Purchase #6	$119.48	7.843%	$128.8508	$128.85	$128.85	$128.90
Purchase #7	$58.38	13.564%	$66.2987	$66.30	$66.30	$66.30
7 purchase totals =	$985.53		$1,095.9097	$1,095.92	$1,095.95	$1,095.90