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	$96.78	4.702%	$101.3306	$101.33	$101.35	$101.30
Purchase #2	$142.42	4.288%	$148.527	$148.53	$148.55	$148.50
Purchase #3	$99.82	6.756%	$106.5638	$106.56	$106.55	$106.60
Purchase #4	$57.82	13.408%	$65.5725	$65.57	$65.55	$65.60
Purchase #5	$27.27	9.779%	$29.9367	$29.94	$29.95	$29.90
Purchase #6	$95.58	10.553%	$105.6666	$105.67	$105.65	$105.70
Purchase #7	$248.32	12.847%	$280.2217	$280.22	$280.20	$280.20
7 purchase totals =	$768.01		$837.8189	$837.82	$837.80	$837.80