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	$36.28	8.283%	$39.2851	$39.29	$39.30	$39.30
Purchase #2	$40.51	4.466%	$42.3192	$42.32	$42.30	$42.30
Purchase #3	$89.79	12.844%	$101.3226	$101.32	$101.30	$101.30
Purchase #4	$30.64	4.494%	$32.017	$32.02	$32.00	$32.00
Purchase #5	$86.96	7.323%	$93.3281	$93.33	$93.35	$93.30
Purchase #6	$143.31	13.724%	$162.9779	$162.98	$163.00	$163.00
Purchase #7	$250.55	11.866%	$280.2803	$280.28	$280.30	$280.30
7 purchase totals =	$678.04		$751.5302	$751.54	$751.55	$751.50