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	$160.64	8.543%	$174.3635	$174.36	$174.35	$174.40
Purchase #2	$115.68	11.132%	$128.5575	$128.56	$128.55	$128.60
Purchase #3	$40.67	4.604%	$42.5424	$42.54	$42.55	$42.50
Purchase #4	$179.44	11.795%	$200.6049	$200.60	$200.60	$200.60
Purchase #5	$166.43	10.693%	$184.2264	$184.23	$184.25	$184.20
Purchase #6	$174.54	9.569%	$191.2417	$191.24	$191.25	$191.20
Purchase #7	$240.26	12.525%	$270.3526	$270.35	$270.35	$270.40
7 purchase totals =	$1,077.66		$1,191.8890	$1,191.88	$1,191.90	$1,191.90