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	$59.28	12.413%	$66.6384	$66.64	$66.65	$66.60
Purchase #2	$250.59	13.494%	$284.4046	$284.40	$284.40	$284.40
Purchase #3	$182.57	7.514%	$196.2883	$196.29	$196.30	$196.30
Purchase #4	$220.76	13.628%	$250.8452	$250.85	$250.85	$250.80
Purchase #5	$87.72	11.236%	$97.5762	$97.58	$97.60	$97.60
Purchase #6	$130.62	10.550%	$144.4004	$144.40	$144.40	$144.40
Purchase #7	$41.65	9.573%	$45.6372	$45.64	$45.65	$45.60
7 purchase totals =	$973.19		$1,085.7903	$1,085.80	$1,085.85	$1,085.70