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	$230.40	10.741%	$255.1473	$255.15	$255.15	$255.10
Purchase #2	$193.25	10.140%	$212.8456	$212.85	$212.85	$212.80
Purchase #3	$73.87	11.404%	$82.2941	$82.29	$82.30	$82.30
Purchase #4	$14.65	7.627%	$15.7674	$15.77	$15.75	$15.80
Purchase #5	$80.34	7.165%	$86.0964	$86.10	$86.10	$86.10
Purchase #6	$147.80	13.360%	$167.5461	$167.55	$167.55	$167.50
Purchase #7	$151.68	5.413%	$159.8904	$159.89	$159.90	$159.90
7 purchase totals =	$891.99		$979.5873	$979.60	$979.60	$979.50