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	$249.47	12.398%	$280.3993	$280.40	$280.40	$280.40
Purchase #2	$141.62	3.633%	$146.7651	$146.77	$146.75	$146.80
Purchase #3	$239.72	3.508%	$248.1294	$248.13	$248.15	$248.10
Purchase #4	$146.51	13.319%	$166.0237	$166.02	$166.00	$166.00
Purchase #5	$55.31	7.651%	$59.5418	$59.54	$59.55	$59.50
Purchase #6	$51.79	11.165%	$57.5724	$57.57	$57.55	$57.60
Purchase #7	$65.59	4.316%	$68.4209	$68.42	$68.40	$68.40
7 purchase totals =	$950.01		$1,026.8526	$1,026.85	$1,026.80	$1,026.80