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	$39.84	13.700%	$45.2981	$45.30	$45.30	$45.30
Purchase #2	$38.31	6.406%	$40.7641	$40.76	$40.75	$40.80
Purchase #3	$172.89	6.751%	$184.5618	$184.56	$184.55	$184.60
Purchase #4	$42.27	11.546%	$47.1505	$47.15	$47.15	$47.20
Purchase #5	$95.76	12.643%	$107.8669	$107.87	$107.85	$107.90
Purchase #6	$168.31	10.170%	$185.4271	$185.43	$185.45	$185.40
Purchase #7	$219.73	5.524%	$231.8679	$231.87	$231.85	$231.90
7 purchase totals =	$777.11		$842.9364	$842.94	$842.90	$843.10