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	$151.27	13.375%	$171.5024	$171.50	$171.50	$171.50
Purchase #2	$243.28	5.398%	$256.4123	$256.41	$256.40	$256.40
Purchase #3	$166.67	7.722%	$179.5403	$179.54	$179.55	$179.50
Purchase #4	$158.33	8.203%	$171.3178	$171.32	$171.30	$171.30
Purchase #5	$105.39	12.557%	$118.6238	$118.62	$118.60	$118.60
Purchase #6	$40.71	8.751%	$44.2725	$44.27	$44.25	$44.30
Purchase #7	$102.47	10.183%	$112.9045	$112.90	$112.90	$112.90
7 purchase totals =	$968.12		$1,054.5736	$1,054.56	$1,054.50	$1,054.50