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	$150.43	6.611%	$160.3749	$160.37	$160.35	$160.40
Purchase #2	$123.82	3.443%	$128.0831	$128.08	$128.10	$128.10
Purchase #3	$50.61	7.873%	$54.5945	$54.59	$54.60	$54.60
Purchase #4	$82.32	8.771%	$89.5403	$89.54	$89.55	$89.50
Purchase #5	$232.79	10.740%	$257.7916	$257.79	$257.80	$257.80
Purchase #6	$209.26	9.615%	$229.3803	$229.38	$229.40	$229.40
Purchase #7	$95.30	3.486%	$98.6222	$98.62	$98.60	$98.60
7 purchase totals =	$944.53		$1,018.3869	$1,018.37	$1,018.40	$1,018.40