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	$71.79	8.787%	$78.0982	$78.10	$78.10	$78.10
Purchase #2	$235.70	5.680%	$249.0878	$249.09	$249.10	$249.10
Purchase #3	$33.65	4.576%	$35.1898	$35.19	$35.20	$35.20
Purchase #4	$245.87	7.474%	$264.2463	$264.25	$264.25	$264.20
Purchase #5	$39.68	13.714%	$45.1217	$45.12	$45.10	$45.10
Purchase #6	$10.48	13.224%	$11.8659	$11.87	$11.85	$11.90
Purchase #7	$193.54	11.461%	$215.7216	$215.72	$215.70	$215.70
7 purchase totals =	$830.71		$899.3313	$899.34	$899.30	$899.30