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	$181.30	4.175%	$188.8693	$188.87	$188.85	$188.90
Purchase #2	$93.81	13.137%	$106.1338	$106.13	$106.15	$106.10
Purchase #3	$143.41	4.223%	$149.4662	$149.47	$149.45	$149.50
Purchase #4	$25.48	5.702%	$26.9329	$26.93	$26.95	$26.90
Purchase #5	$96.85	12.680%	$109.1306	$109.13	$109.15	$109.10
Purchase #6	$81.53	10.538%	$90.1216	$90.12	$90.10	$90.10
Purchase #7	$98.57	6.111%	$104.5936	$104.59	$104.60	$104.60
7 purchase totals =	$720.95		$775.2480	$775.24	$775.25	$775.20