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	$19.81	9.834%	$21.7581	$21.76	$21.75	$21.80
Purchase #2	$52.77	13.531%	$59.9103	$59.91	$59.90	$59.90
Purchase #3	$67.89	8.796%	$73.8616	$73.86	$73.85	$73.90
Purchase #4	$145.65	3.746%	$151.106	$151.11	$151.10	$151.10
Purchase #5	$153.56	9.793%	$168.5981	$168.60	$168.60	$168.60
Purchase #6	$80.96	13.138%	$91.5965	$91.60	$91.60	$91.60
Purchase #7	$152.71	10.402%	$168.5949	$168.59	$168.60	$168.60
7 purchase totals =	$673.35		$735.4255	$735.43	$735.40	$735.50