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	$236.85	13.115%	$267.9129	$267.91	$267.90	$267.90
Purchase #2	$89.66	11.341%	$99.8283	$99.83	$99.85	$99.80
Purchase #3	$199.46	5.256%	$209.9436	$209.94	$209.95	$209.90
Purchase #4	$196.99	8.429%	$213.5943	$213.59	$213.60	$213.60
Purchase #5	$236.36	5.177%	$248.5964	$248.60	$248.60	$248.60
Purchase #6	$117.75	8.263%	$127.4797	$127.48	$127.50	$127.50
Purchase #7	$159.25	5.838%	$168.547	$168.55	$168.55	$168.50
7 purchase totals =	$1,236.32		$1,335.9022	$1,335.90	$1,335.95	$1,335.80