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	$98.58	7.356%	$105.8315	$105.83	$105.85	$105.80
Purchase #2	$76.59	12.458%	$86.1316	$86.13	$86.15	$86.10
Purchase #3	$196.57	11.118%	$218.4247	$218.42	$218.40	$218.40
Purchase #4	$243.35	10.383%	$268.617	$268.62	$268.60	$268.60
Purchase #5	$19.77	10.863%	$21.9176	$21.92	$21.90	$21.90
Purchase #6	$87.92	3.641%	$91.1212	$91.12	$91.10	$91.10
Purchase #7	$52.39	11.874%	$58.6108	$58.61	$58.60	$58.60
7 purchase totals =	$775.17		$850.6544	$850.65	$850.60	$850.50