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	$209.51	6.762%	$223.6771	$223.68	$223.70	$223.70
Purchase #2	$118.87	10.691%	$131.5784	$131.58	$131.60	$131.60
Purchase #3	$93.46	6.544%	$99.576	$99.58	$99.60	$99.60
Purchase #4	$5.64	13.148%	$6.3815	$6.38	$6.40	$6.40
Purchase #5	$167.40	4.247%	$174.5095	$174.51	$174.50	$174.50
Purchase #6	$219.39	5.847%	$232.2177	$232.22	$232.20	$232.20
Purchase #7	$18.78	13.859%	$21.3827	$21.38	$21.40	$21.40
7 purchase totals =	$833.05		$889.3229	$889.33	$889.40	$889.40