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	$89.54	12.682%	$100.8955	$100.90	$100.90	$100.90
Purchase #2	$169.85	6.379%	$180.6847	$180.68	$180.70	$180.70
Purchase #3	$183.99	11.358%	$204.8876	$204.89	$204.90	$204.90
Purchase #4	$179.39	10.848%	$198.8502	$198.85	$198.85	$198.90
Purchase #5	$196.45	5.532%	$207.3176	$207.32	$207.30	$207.30
Purchase #6	$150.67	9.813%	$165.4552	$165.46	$165.45	$165.50
Purchase #7	$33.31	5.303%	$35.0764	$35.08	$35.10	$35.10
7 purchase totals =	$1,003.20		$1,093.1672	$1,093.18	$1,093.20	$1,093.30