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	$150.25	13.386%	$170.3625	$170.36	$170.35	$170.40
Purchase #2	$14.68	6.728%	$15.6677	$15.67	$15.65	$15.70
Purchase #3	$78.45	9.488%	$85.8933	$85.89	$85.90	$85.90
Purchase #4	$165.34	10.255%	$182.2956	$182.30	$182.30	$182.30
Purchase #5	$33.40	11.357%	$37.1932	$37.19	$37.20	$37.20
Purchase #6	$223.38	7.713%	$240.6093	$240.61	$240.60	$240.60
Purchase #7	$79.83	3.491%	$82.6169	$82.62	$82.60	$82.60
7 purchase totals =	$745.33		$814.6385	$814.64	$814.60	$814.70