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	$110.50	11.558%	$123.2716	$123.27	$123.25	$123.30
Purchase #2	$185.48	6.285%	$197.1374	$197.14	$197.15	$197.10
Purchase #3	$127.77	4.467%	$133.4775	$133.48	$133.50	$133.50
Purchase #4	$80.82	5.775%	$85.4874	$85.49	$85.50	$85.50
Purchase #5	$88.49	3.297%	$91.4075	$91.41	$91.40	$91.40
Purchase #6	$209.43	7.854%	$225.8786	$225.88	$225.90	$225.90
Purchase #7	$19.61	11.747%	$21.9136	$21.91	$21.90	$21.90
7 purchase totals =	$822.10		$878.5736	$878.58	$878.60	$878.60