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	$134.54	9.652%	$147.5258	$147.53	$147.55	$147.50
Purchase #2	$92.86	13.199%	$105.1166	$105.12	$105.10	$105.10
Purchase #3	$24.71	10.203%	$27.2312	$27.23	$27.25	$27.20
Purchase #4	$248.70	11.553%	$277.4323	$277.43	$277.45	$277.40
Purchase #5	$104.84	4.460%	$109.5159	$109.52	$109.50	$109.50
Purchase #6	$74.52	7.444%	$80.0673	$80.07	$80.05	$80.10
Purchase #7	$166.47	3.103%	$171.6356	$171.64	$171.65	$171.60
7 purchase totals =	$846.64		$918.5247	$918.54	$918.55	$918.40