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	$138.47	9.419%	$151.5125	$151.51	$151.50	$151.50
Purchase #2	$95.86	11.460%	$106.8456	$106.85	$106.85	$106.80
Purchase #3	$169.76	6.189%	$180.2664	$180.27	$180.25	$180.30
Purchase #4	$250.53	8.537%	$271.9177	$271.92	$271.90	$271.90
Purchase #5	$67.92	7.319%	$72.8911	$72.89	$72.90	$72.90
Purchase #6	$180.87	4.502%	$189.0128	$189.01	$189.00	$189.00
Purchase #7	$109.86	8.156%	$118.8202	$118.82	$118.80	$118.80
7 purchase totals =	$1,013.27		$1,091.2663	$1,091.27	$1,091.20	$1,091.20