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	$94.71	6.418%	$100.7885	$100.79	$100.80	$100.80
Purchase #2	$58.71	9.219%	$64.1225	$64.12	$64.10	$64.10
Purchase #3	$166.27	11.382%	$185.1949	$185.19	$185.20	$185.20
Purchase #4	$119.78	5.865%	$126.8051	$126.81	$126.80	$126.80
Purchase #5	$147.75	7.526%	$158.8697	$158.87	$158.85	$158.90
Purchase #6	$167.96	9.110%	$183.2612	$183.26	$183.25	$183.30
Purchase #7	$174.68	5.803%	$184.8167	$184.82	$184.80	$184.80
7 purchase totals =	$929.86		$1,003.8586	$1,003.86	$1,003.80	$1,003.90