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	$14.86	13.758%	$16.9044	$16.90	$16.90	$16.90
Purchase #2	$184.51	10.170%	$203.2747	$203.27	$203.25	$203.30
Purchase #3	$137.26	13.118%	$155.2658	$155.27	$155.25	$155.30
Purchase #4	$103.64	11.827%	$115.8975	$115.90	$115.90	$115.90
Purchase #5	$210.56	12.521%	$236.9242	$236.92	$236.90	$236.90
Purchase #6	$89.25	10.301%	$98.4436	$98.44	$98.45	$98.40
Purchase #7	$87.56	13.446%	$99.3333	$99.33	$99.35	$99.30
7 purchase totals =	$827.64		$926.0435	$926.03	$926.00	$926.00