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	$239.47	13.558%	$271.9373	$271.94	$271.95	$271.90
Purchase #2	$94.27	10.148%	$103.8365	$103.84	$103.85	$103.80
Purchase #3	$87.76	8.625%	$95.3293	$95.33	$95.35	$95.30
Purchase #4	$246.59	3.635%	$255.5535	$255.55	$255.55	$255.60
Purchase #5	$24.54	11.256%	$27.3022	$27.30	$27.30	$27.30
Purchase #6	$234.59	12.829%	$264.6856	$264.69	$264.70	$264.70
Purchase #7	$54.60	6.736%	$58.2779	$58.28	$58.30	$58.30
7 purchase totals =	$981.82		$1,076.9223	$1,076.93	$1,077.00	$1,076.90