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	$59.90	3.362%	$61.9138	$61.91	$61.90	$61.90
Purchase #2	$250.65	11.778%	$280.1716	$280.17	$280.15	$280.20
Purchase #3	$58.88	4.634%	$61.6085	$61.61	$61.60	$61.60
Purchase #4	$59.81	7.214%	$64.1247	$64.12	$64.10	$64.10
Purchase #5	$25.32	7.305%	$27.1696	$27.17	$27.15	$27.20
Purchase #6	$37.46	10.456%	$41.3768	$41.38	$41.40	$41.40
Purchase #7	$52.66	13.170%	$59.5953	$59.60	$59.60	$59.60
7 purchase totals =	$544.68		$595.9603	$595.96	$595.90	$596.00