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	$146.42	9.810%	$160.7838	$160.78	$160.80	$160.80
Purchase #2	$243.50	11.682%	$271.9457	$271.95	$271.95	$271.90
Purchase #3	$180.38	3.400%	$186.5129	$186.51	$186.50	$186.50
Purchase #4	$249.99	8.670%	$271.6641	$271.66	$271.65	$271.70
Purchase #5	$32.25	7.709%	$34.7362	$34.74	$34.75	$34.70
Purchase #6	$77.75	6.621%	$82.8978	$82.90	$82.90	$82.90
Purchase #7	$39.27	6.582%	$41.8548	$41.85	$41.85	$41.90
7 purchase totals =	$969.56		$1,050.3953	$1,050.39	$1,050.40	$1,050.40