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	$31.35	12.139%	$35.1556	$35.16	$35.15	$35.20
Purchase #2	$93.53	6.400%	$99.5159	$99.52	$99.50	$99.50
Purchase #3	$92.75	6.440%	$98.7231	$98.72	$98.70	$98.70
Purchase #4	$80.51	7.220%	$86.3228	$86.32	$86.30	$86.30
Purchase #5	$18.94	3.396%	$19.5832	$19.58	$19.60	$19.60
Purchase #6	$199.96	3.280%	$206.5187	$206.52	$206.50	$206.50
Purchase #7	$137.92	9.759%	$151.3796	$151.38	$151.40	$151.40
7 purchase totals =	$654.96		$697.1989	$697.20	$697.15	$697.20