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	$180.83	4.741%	$189.4032	$189.40	$189.40	$189.40
Purchase #2	$83.96	7.118%	$89.9363	$89.94	$89.95	$89.90
Purchase #3	$152.28	11.370%	$169.5942	$169.59	$169.60	$169.60
Purchase #4	$107.63	5.526%	$113.5776	$113.58	$113.60	$113.60
Purchase #5	$67.67	6.206%	$71.8696	$71.87	$71.85	$71.90
Purchase #6	$72.49	8.274%	$78.4878	$78.49	$78.50	$78.50
Purchase #7	$189.61	8.245%	$205.2433	$205.24	$205.25	$205.20
7 purchase totals =	$854.47		$918.1120	$918.11	$918.15	$918.10