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	$102.39	13.346%	$116.055	$116.06	$116.05	$116.10
Purchase #2	$176.50	6.442%	$187.8701	$187.87	$187.85	$187.90
Purchase #3	$235.26	12.476%	$264.611	$264.61	$264.60	$264.60
Purchase #4	$154.63	4.781%	$162.0229	$162.02	$162.00	$162.00
Purchase #5	$26.36	10.206%	$29.0503	$29.05	$29.05	$29.10
Purchase #6	$216.26	3.387%	$223.5847	$223.58	$223.60	$223.60
Purchase #7	$81.38	10.397%	$89.8411	$89.84	$89.85	$89.80
7 purchase totals =	$992.78		$1,073.0351	$1,073.03	$1,073.00	$1,073.10