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	$89.69	11.334%	$99.8555	$99.86	$99.85	$99.90
Purchase #2	$196.33	4.221%	$204.6171	$204.62	$204.60	$204.60
Purchase #3	$115.51	6.784%	$123.3462	$123.35	$123.35	$123.30
Purchase #4	$120.77	10.819%	$133.8361	$133.84	$133.85	$133.80
Purchase #5	$136.78	7.542%	$147.0959	$147.10	$147.10	$147.10
Purchase #6	$69.93	4.735%	$73.2412	$73.24	$73.25	$73.20
Purchase #7	$196.66	11.126%	$218.5404	$218.54	$218.55	$218.50
7 purchase totals =	$925.67		$1,000.5324	$1,000.55	$1,000.55	$1,000.40