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	$92.57	11.654%	$103.3581	$103.36	$103.35	$103.40
Purchase #2	$151.80	13.447%	$172.2125	$172.21	$172.20	$172.20
Purchase #3	$105.46	4.228%	$109.9188	$109.92	$109.90	$109.90
Purchase #4	$107.39	7.351%	$115.2842	$115.28	$115.30	$115.30
Purchase #5	$47.83	11.445%	$53.3041	$53.30	$53.30	$53.30
Purchase #6	$142.57	9.812%	$156.559	$156.56	$156.55	$156.60
Purchase #7	$131.96	5.305%	$138.9605	$138.96	$138.95	$139.00
7 purchase totals =	$779.58		$849.5972	$849.59	$849.55	$849.70