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	$99.97	12.696%	$112.6622	$112.66	$112.65	$112.70
Purchase #2	$137.55	11.168%	$152.9116	$152.91	$152.90	$152.90
Purchase #3	$212.97	12.739%	$240.1002	$240.10	$240.10	$240.10
Purchase #4	$207.47	3.675%	$215.0945	$215.09	$215.10	$215.10
Purchase #5	$109.34	8.414%	$118.5399	$118.54	$118.55	$118.50
Purchase #6	$94.62	4.836%	$99.1958	$99.20	$99.20	$99.20
Purchase #7	$218.86	3.220%	$225.9073	$225.91	$225.90	$225.90
7 purchase totals =	$1,080.78		$1,164.4115	$1,164.41	$1,164.40	$1,164.40